PT User`s Manual - The Comport Computing Company
Contents
1. i e drawdown tests Pressure is plotted versus the logarithm of flowing time 2 Horner analysis for wells that were flowing and were shut in i e buildup tests Pressure is plotted versus the logarithm of shut in time divided by total flowing and shut in time In both cases the slope of the pressure vs log of time is proportional to the flow rate PT User s Manual Page 14 permeability thickness and fluid viscosity In addition the intercept of the logarithmic line is an indication of the near wellbore damage skin Semilog analysis can be done by selecting Analysis Classical Semilog from the menu Classical Square Root of Time Analysis F sart rime Analysis C RON omm Q H v Y dh x Method Sqrt Time d cd Q Well Examples Test Infinite Cond Fracture Gringarten et al SPE 5496 Table 1 3700 Pw psia Analysis m 6 65019 psia hr 0 5 Pw 1 3517 8 psia Results kx 2 3992952 mdft 2 5 10 Sart Time hr 0 5 Points 5 1 95 3457 35 Std Dev 1 246 oquare root of time analysis uses a graph of pressure versus the square root of time This usually applies only to wells with vertical hydraulic fractures where the early time transient flow is dominated by linear flow into the fracture The slope of the pressure versus square root of time is proportional to the permeability and fracture length squared Note that superposition may be applied but strictly superposition should only be used when there was short flo2. Data menu contains functions to create and edit wells well tests and test data PT User s Manual Page 1 The Analysis menu allows the various analysis methods to be chosen The Design menu allows the design of well tests The Configure menu provides the option to automatically load the last project when PT is started The Language menu allows the use of either English or Spanish text on all of the windows in PT To change the language simply select the desired language from the menu The Help menu allows information concerning the version of PT to be displayed To see the version information select Help About PT User s Manual Page 2 Getting Started To start using PT it is necessary to open or define a project Defining a project creates a database which will contain all of the data needed to evaluate well tests It should be noted that RESys uses a Microsoft Jet database by default That means that there s nothing special to install or configure since Jet drivers are normally included in Microsoft Windows It s the same database format used by Microsoft Access Once any RESys module including PT is installed it is ready to use without any further hassles unless you decide to use a different database format The remainder of this manual assumes that the default Jet database is used Creating a Project To create a new project select Project New from the menu You will need to select a directory and a filename from the fi
3. actual data of interest begins at 1 hour and ends at around 6 5 hours and consists of 6 increasing injection rates followed by a short fall off The data before 1 hour includes pressures measured at the surface and while running the gage in the well including gradient stops The data after about 6 5 hour includes data measured coming out of the well and at the surface The data can be interactively edited using a variety of functions available on the buttons in the toolbar at the top of the window From the left side the buttons perform the following functions X Mouse Zooms puts the mouse in zoom mode and changes the cursor to 4 arrows Dragging the mouse will select an area and zoom the display Mouse Selects puts the mouse into selection mode and changes the cursor to cross hairs This is the default mode where dragging the mouse selects all of the points in the selected area I Zoom Reset Resets the scales on the display to show all of the data points Select All Selects all of the points Clear Selection Unselects all of the points d Invert Selection Changes all selected point to unselected and vice versa X Delete Points Deletes all of the selected points KH Set Time 0 Shifts all of the data so that the first point becomes time O for the test 9 Accept Changes Applies the changes made so far and replaces the test data with the currently displayed data points This cannot
4. 25 69 767 512 02 Std Dev 2 552511 PT User s Manual Page 17 Well Test Design PT can be used to design well tests by entering estimated reservoir and well parameters and generating the theoretical pressure response To use the test design features in PT create a well and test as explained in the previous section Fluid and Rock properties as well as Rates should be entered Once the basic test data has been defined select Design from the menu On the form the type of well and reservoir can be selected and the parameters may be adjusted to see the expected pressure response The pressure response can be used to help in test design PT User s Manual Page 18 Technical Description Fluid Types and Pseudopressure PT is internally formulated in terms of a generalized pseudopressure so that most types of reservoir fluids can be properly handled In this version of PT the fluid systems supported are Normal Oil Compressible Oil Ideal Gas and Real Gas The only difference between the models is the definition of pseudopressure which is used internally As shown by P S Fair Investigation of the Diffusivity Equation with General Pressure Dependent Rock and Fluid Properties submitted to SPE Dec 1991 the diffusivity equation can be written in terms of a general pseudopressure function which applies not only to gases but to any type of fluid and rock system where the physical properties vary with resp
5. RESys Reservoir Evaluation System PT Pressure Transient Analysis Users Manual fo Copyright 2006 2010 The Comport Computing Company All Rights Reserved RESys is an integrated software system for performing oil and gas reservoir evaluations Based on an integrated database and using object oriented software design techniques RESys is a modular and extensible software system consisting of various specialized modules for the analysis and evaluation of well logs core data production data and more The modular integrated design allows the system to be extensible so that additional modules can be added without requiring a rewrite or redesign of the rest of the system In addition due to the modularity and integrated database individual modules can be optimized RESys is designed as a standalone yet integrated system Each module can be used by itself however the full power of integrated software is unleashed when the various modules are combined PT comprises the module allowing the analysis of pressure transient well tests As a standalone program it allows the evaluation and organization of well test data and interpretations but PT is fully integrated with the production related modules in RESys so the interpretations are available for use in an integrated evaluation of a reservoir or field At Comport Computing we value the comments and suggestions of our software users If you find a bug please let us know We ll fix it as f
6. TTMTTMMTMTMM 16 Wel TESTE DESIGN wetness vee wieviaresseneceataanasyaneaaes a N 18 TECHNICAL DES ERP HO Rare desert icd rue ced Ee tue De ce tr e ede ec erus 19 Fluid Types and PseugdoDreSSUle eie esurire tiit oin poa oco p quo poscit ees pace peuopde2o ise poes 19 Pressure TransienmEduallOllS 2 929 99 9 aaea robado pruu de De rdU ed opo bd aus 21 An Overview of Pressure Transient Methods cccccseeceeeeeeeeeseeeeseeeeseeeesaneesaeeeens 23 Computation of Pressure Derivatives seeessesesssesseeeeenn ener 24 Overview PT is a system for organizing and analyzing pressure transient well test data and interpretations The system consists of a database along with tools to aid in the entry of data and interpretations RESys is based on so called projects which represent data that are somehow related You can create as many projects as you want and organize them in whatever way makes sense for your purpose For example for pressure transient data perhaps a project would consist of all of the tests in a given oil field On the other hand for a student a project might be all of the tests done during a class or in conjunction with a project It really is up to you as to how you want to organize your projects and data It is important to understand that the project database contains all of the information needed for well test evaluations If you need to make a backup of the project simply copy the project databa
7. ast as possible and send you a free updated copy of the software In addition if you suggest an enhancement which we implement you ll receive a free upgrade to the new version Corrections or comments on RESys PT or this manual should be directed to software comportco com Table of Contents 9 1 Getting otal Cee TTD DT a a 3 eand o PELO e Gb eaaa A deerat ete etu 3 Openng an Exis ind PEL teo esu o epu e e oua Iaceo RN 3 When a Project is Opened the First Time ccccceecccceeceeceeeeseeeeeseeeeessaeeesseeesseeeesaaes 4 SATSES ll ate a Well E 4 eii seEcRII NIE SERENE SEES a a E EE EEEE i i 5 MADONIN G PIE VVell TESIS rere E EAO 6 E ANONO OSCE Ib a lclninciiadacdunaadactaacnsautended Magsuenabassanna ERE NES terc dto rod bran ER 6 IMPORINGE PLESS FE Ae ea ennen e EENE EEE EEEE EEEE 7 Editing Raw Gage DIS aee AR AE IRR ERREN 8 EnEnng ICSU ALCS PNE UU UE 9 Fluid and ROCK PFODCMICS ipinasa E RE 11 SUING I r E a M m 13 classical Ganesan ATalyslS salsa pube auda mtu eter Et dot Ea det LOS ente an o I Ee tO eoo 13 Classical oemilog Andy SIS ieexixeudeix tete itecto oet ener ete pe pde va pate dee pene e vete p tu pee EUR e be 14 Classical Square Root of Time Analysis acsi 15 Type Curve Analysis essseesssessssseeeeeeee nennen enn enean nnn nnns na rnnt nnn 15 micis RIT SIS EET NETTE TU T
8. be undone HM Undo Changes Throw away any changes made since the last Accept Changes After making any changes to the data interactively be sure to Accept Changes 2 then close the P T Test Data form by pressing the Ok button Entering Test Rates All pressure transient well tests require a set of test rates to be defined In PT the well producing or injection rates are divided into two sets the rate history prior to the start of the test and the rates during the test Note that in PT production rates are defined as positive and injection rates are negative In PT the times for the rates are expressed as time intervals in the order of occurrence For example in the illustration on the right below 3 time intervals are shown before the test each lasting for 3 hours followed by a shut in i e buildup Only the data during the buildup was recorded and can be analyzed in PT To enter the test rates select Data Rates from the menu and enter the rates in the Prior to Test and During Test panels on the dialog as shown in the following illustration Note that the PT User s Manual Page 9 following simple cases require the following rate data Buildup Test Enter the producing time and producing rate Prior to Test and zeros for During Test Injection Falloff Test Enter the injection time and negative injection rate Prior to Test and zero during Test Drawdown Test Leave the Prior to Test columns blank and enter t
9. checked If you need to change the information later simply select the well from the list and then select Data Well Edit from the menu Wells can also be deleted by selecting the well from the list and then selecting Data Well Delete from the menu PT User s Manual Page 4 a Well Data Comport Computing None Location Various UWI X Coord Y Coord Latitude Longitude Hevation Total Depth Drill Date Abnd Date Creating a Well Test To create a new Well Test select Data Test New from the menu and enter the basic information in the PT Test dialog If you need to change the data later select the well test from the right panel of the main form and then select Data Test Edit Similarly a test can be deleted by selecting the test and then selecting Data Test Delete from the menu PT Test Well Examples Date 728 200 Tile New PT Test Test Fluid Rw 0 Thickness 0 Porosity 0 0 Gage Depth mm PT User s Manual Page 5 Importing PT4 Well Tests If you have data from a previous version of PT it is possible to import the data for use in RESys PT however there are several differences between the data used in previous versions SO some rearrangement will be needed To import PT4 data saved in dat files select Data Test Import PT4 File from the menu and then select the files to be imported If it doesn t already exist a pseudo well named PT4Import will be created and the imported test data
10. ds to the slope on a semi log plot which always has more visual curve character than that of a log log plot since the process of taking the logarithm of pressure differences also removes most character from the data Before development of the pressure derivative techniques semi log methods were deemed more reliable for transient analyses due to this loss of characteristic curvature with log log methods Unfortunately taking the derivative of measured pressure data is not trivial The simplest approach would be to simply divide each pair of pressure readings by the difference in log time however except for ideal data the resulting values nearly always have a high degree of scatter The scatter is due to round off and measurement errors and makes use of the derivative information impractical ae R where p is the value Cix1 ti measured at time t If we expand with a Taylor series and add a small error we obtain A two point method for estimating a derivative is f t 1 1 Pi Pi At p t 5 At p t e Ate p t ut Pi 1 Pi 1 1 t At p t At Ct Lm p gt pots p t uae Pi 1 Di 1 1 t Atv t At VE ENES p t AR Atp t a AUD t a When the second derivative term is small the error is dominated by m and since At should be small the error can be very large To counteract this problem a more complex algori
11. e real gas model fluid density is expressed in terms of the real gas equation of state and the viscosity is assumed to vary arbitrarily with pressure Both the real gas z factor and viscosity must be specified versus pressure To maintain consistency with the standard literature definition of real gas pseudopressure a factor of 2 is introduced so the arbitrary constant c 0 5 This yields the following expression for pseudopressure p mp 2 dp po H4 1 2rkTo 2 qpor 70 Mp Ideal Gas In the ideal gas fluid model the z factor and viscosity in the real gas model are assumed to be constant In this special case the integral can be evaluated directly yielding a pseudopressure function proportional to p This gives the standard p formulation which is commonly used for gas wells at low pressure In this case the pseudopressure definition becomes m p p pf 1 2mzkTy 2 quzpoT mp PT User s Manual Page 20 Pressure Transient Equations The basic relations for pressure transient analysis consist of the diffusivity equation to describe flow within the reservoir along with suitable boundary conditions to describe flow at the outer edge of the reservoir as well as into the wellbore In most cases the reservoir is assumed to be infinite so the outer boundary condition is especially simple To simplify and standardize the diffusivity equation and boundary conditions dimensionless parameters are defined T
12. ect to pressure The use of this general pseudopressure function greatly simplifies the formulation of pressure transient analysis methods In PT the form of the general pseudopressure function is p p m p dp Do 2mkh Mp c m mj where c is an arbitrary constant Using this general definition the typical types of fluids normally encountered in practice can be handled by simply defining the appropriate relationships for density and viscosity for each fluid type and then evaluating the resulting integral Normal Oil The normal oil model uses the standard assumptions of constant fluid viscosity and small constant fluid compressibility In this case the integral simplifies to kp p pg u Note that the density ratio is the definition of Bo and defining the arbitrary constant c 1 gives the standard definition of dimensionless pressure In this case the pseudopressure and pressure are identical m p p pi oa mp qBu D Pi Compressible Oil In the compressible oil fluid model we remove the assumption of small compressibility but still assume that both viscosity and compressibility are constant The fluid density is given by PT User s Manual Page 19 the relation p pge 9 where cis the fluid compressibility In this case the integral can be evaluated analytically and the pseudopressure becomes 1 m p 1 ecf P Po Cf B 2mkh D qBu m mj Real Gas In th
13. es one of determining what values of the dimensionless variables and parameters are needed to achieve a match between the theoretical solutions and the measured data This can be done in several ways leading to the three major methods used in pressure transient analysis and implemented in the PT software Classical analysis methods rely on the observation that portions of the theoretical pressure solutions form straight lines when plotted versus some type of time related variable The Cartesian plot is useful at early times when wellbore storage dominates and inflow from the reservoir is essentially filling the wellbore It is also useful at very late times when production is draining the reservoir and the average reservoir pressure is dropping with time The square root of time plot is useful when transient linear flow dominates usually due to flow into a vertical fracture intersecting the wellbore The semilog methods are useful during transient radial flow after wellbore effects have died out In any of the methods fitting a straight line to the data is one way to determine the parameters required to make the solution match the data The slope and intercept of the fitted line are used to compute the physical parameters Type curve analysis relies on the observation that the dimensionless time and pressure parameters consist of a constant term multiplied by real time or pressure and the fact that multiplying numbers is equivalent to adding logarithm
14. ess Permeability Pressure Flow rate Radius Skin factor Time Length Phase redistribution time parameter Porosity Viscosity apparent dimensionless fracture initial surface total well phase redistribution PT User s Manual Page 22 An Overview of Pressure Transient Methods The mathematical basis of pressure transient analysis lies in the partial differential equations of single phase fluid flow Since we are concerned mainly with the pressure response at a producing well during time periods when wellbore effects may be important the radial form of the diffusivity equation is usually used to model the reservoir flow behavior Since wellbore effects are important mass and momentum balance relations for fluids in the wellbore describe the wellbore boundary conditions Since the reservoir is normally extremely large in comparison with the size of the wellbore an infinite reservoir is often assumed In order to keep from solving the equations for every combination of parameters that might be encountered the equations are generally expressed in terms of dimensionless quantities Except for a few unusual circumstances the same set of dimensionless parameters are used throughout well test analysis and are described in Appendix I Once the diffusivity equation and the associated boundary conditions are specified in terms of dimensionless variables and a solution is obtained the process of pressure transient analysis becom
15. he definition of these parameters expressed in Darcy units are as follows kt Radius rp Time Up 2 Tw Quctrw khAp _ dw Pressure pp T Hate dwp L5 C Storage Cp E As documented in the paper Generalized Wellbore Effects in Pressure Transient Testing Fair SPE Formation Evaluation June 1996 the general equations for describing flow into and pressure transient behavior within the wellbore during single phase well testing are as follows okin Pwo pp rp 1 Sqyp 9p Reservoir Inflow qup 2 dpyw dp d dw Wellbore qwp 1 Cp Ie 7 p Cmp rd The solution of these wellbore equations along with the appropriate form of the diffusivity equation yields the general relationships used in pressure transient analysis In addition the common forms for the phase redistribution pressure function used in PT are defined as Fair Pop Con 1 e t a Hegeman Pop Cop erf tp ap Using either of these definitions there is a linear early time behavior in the absence of momentum effects which has the appearance of wellbore storage This apparent storage is defined as PT User s Manual Page 21 p Apparent Storage Cap Es i Summary of variables used B C Cm Cy Ct Subscripts SeeTOTFOMSES LS a O aa e Formation volume factor Wellbore storage parameter Wellbore momentum parameter Wellbore phase redistribution parameter Total fluid compressibility Reservoir thickn
16. he production rate at time zero During Test Injection Test Leave the Prior to Test columns blank and enter the negative injection rate at time zero During Test PT Test Rates FE ES PT Test Rates Well Examples Well Examples Test 7 30 2008 Homer Example Eadougher Monograph page Test 7 31 2008 Multi Rate w Buildup Earlougher Example 5 5 Priorto Test During Test Priorto Test During Test Rate Rate Time Rate Time Rate Bbl D Bbl D hr Bbl D Ihr Bbl D 4900 478 5 3 319 3 In contrast to previous versions of PT multiple rates during the test can also be analyzed The following rates illustrate the case of a multiple rate injection test with 6 increasing injection rates 50 100 150 200 250 and 300 for 1 hour each Following 16 minutes 0 28 hours at the final rate 350 the well was shut in and the pressure fall off was also recorded By entering the data as shown below assuming the well was static before the start of the test all of the data can be evaluated PT User s Manual Page 10 P PT Test Rates Well Examples Test 7 28 2010 New PT Test Fror to Test During Test Rate Bbl D Fluid and Rock Properties Every pressure transient test needs rock and fluid properties in order to be analyzed and modeled In PT the rock and fluid properties are entered by selecting the well and test then select Data Fluid Rock from the menu The PVT Data dialog will be displayed allowing the type of fl
17. ing parameters By default no data thinning is performed but in the case of large data sets the data can be thinned by specifying a maximum time interval and a minimum pressure interval For the values of Max DT 1 and Min DP 10 as shown in the example at least 1 point will be read every hour but points less than 10 psia different will be discarded Once the import parameters have been set press the Ok button to import the data Once the data has been read the data editing dialog will be displayed where further data editing can be performed such as the removal of extraneous points before or after the actual test information i e when the gage is being run in and out of the well PT User s Manual Page 7 Editing Raw Gage Data Once the gage data has been imported it is often necessary to edit the data to remove extraneous data such as spurious data points and pressures representing the gage running in and out of the well The simplest way to accomplish that in PT is graphically by pressing the graphics button B on the P T Data form displayed after importing the data If the form isn t showing then select Data T P Data Edit from the menu PT User s Manual P T Test Data Well Examples Tes 7 28 2010 Mew PT Test Time hr Pw psia E 0 3917 1 5 0 404 Graphics Edit Button P T Data Graph AM 9 r amp di XK Well Examples New PT Test Points 615 2 37 4918 63 Page 8 In the example the
18. le selection dialog and then will be asked if you want to create the project Selecting Yes will automatically create the database selecting No will abort with no database created If the selected file already exists you will be asked whether to replace the database Selecting Yes will overwrite the existing file erasing all of its contents Selecting No will abort without doing anything Once the project database is created you will be presented with a dialog to enter the project name as shown Simply add your own project title Click Ok to save the project data or Cancel to accept the default Normally you will want to provide your own name for the project If you need to change the project name later simply select Project Edit from the menu ul RESys Project Mame I A N i e Once the project has been created it will be opened for use Opening an Existing Project If you have an existing RESys project you can open it for use by any module including PT Simply select Project Open from the menu and then choose the project database file from the file selection dialog PT User s Manual Page 3 When a Project is Opened the First Time The first time a module is used with a particular project the RESys system will check to make sure that all needed parameters and units are defined and you will be presented with a dialog allowing the units to be defined as well as a dialog allowing the parameters to be defined Depending on what
19. ly the match point can be entered directly into the tD 1 and pD 1 boxes Based on the position of the curves the permeability thickness product can be estimated while other parameters can be estimated visually from the curves Regression Analysis Regression analysis uses a nonlinear regression technique to fit a theoretical pressure response curve to the observed pressure versus time data by directly adjusting the reservoir and well parameters to minimize the sum of the squared errors Regression analysis can be done by selecting Analysis Regression from the menu The desired graph display cartesian semilog or log log can be chosen from the Graph drop down list The points to be used in the minimization can be selected using the mouse The well and reservoir model to be used as well as the parameters to be optimized can be selected from the tab sheets on the right Selecting the check box next to a parameter will perform a fit using that parameter alone The curve fit button can be used to perform an optimization using all the selected data points with respect to the selected parameters The number of points used and the standard deviation of the curve fit is shown in the bottom PT User s Manual Page 16 status bar PT Regression Analysis E 3 Q w w Y d 27 Graph Loglog Well Well_2 Grid Test Storage Example Rosa Home SPE 22673 Table 1 Derivatives Pw p Model Radial 15 0 1 1 10 dt hr Points
20. modules may have been used before you may see some or all of the following unit and parameter definitions To accept the defaults simply press Ok To change the default units select or type the desired unit name in the Unit column and a conversion factor in the Factor column For example to specify depth in meters use m as the unit name and 3 28084 the number of feet in a meter as the factor To change the default parameter values type the necessary values in the respective Value column Note that once set these values and units definitions cannot be changed since doing so would corrupt the database u Measurement Units Units for this module i o Parameters Unit Type 1 Gas Rate MCF D 1 Gas Volume MCF 1 1 1 Factor Parameter values Parameter Value Units Std Temperature 60 F Liquid Rate Bbl D Liquid Volume bbl MapXY m 1280839 f Permeability md md Porosity fraction fraction After the units have been set PT uses two parameters that will need to be defined As shown in the above dialog the Standard Temperature and Pressure are required and will be used in volume calculations especially for gases Creating a Well Of course a project isn t of much use without data so normally the next step will be to create a well Simply select Data Well New from the menu and enter the descriptive information in the Well Data dialog Note that the Outcrop check box is not used in PT and should be left un
21. ost cases it is much easier to import massive amounts of pressure data directly froma pressure gage data file Any data file that lists time and pressure in columnar ASCII format may be imported directly into PT To import test data select eh well and test on the main form then select Data T P Data Import Gage Data from the menu On the file selection dialog select the file containing the data and press the Open button The file will be read and the Import Gage Data dialog will be displayed showing the import parameters and a preview of the data file as illustrated below cs rm Import Gage Data File Skip 1st Columns Time 1 EARESys NETXP Tbin x86 Debug S TARTEST REC 2 lines Time Format Hours Minutes HH MM 55 Thinning Max DT 1 Pressure Z Min DP 1 Cancel Ok 12 07 31 10 00 00 SPRESSURE 3 0 0000 4 0 0042 05 0 0083 06 0 0125 7 040167 08 0 0333 09 0 0500 10 0 0667 0 0833 0 1000 X 0 1167 14 0 1333 14 84 54 4 14 50 64 37 14 50 64 40 14 50 64 33 14 50 54 4 14 50 64 48 14 50 64 52 14 50 64 52 14 50 64 52 14 50 64 52 14 50 64 54 14 50 65 15 5 0 1500 0 1667 14 50 65 66 14 50 65 90 The file preview shown in the bottom half of the dialog displays the line numbers followed by the data Before importing select the number of lines at the start of the file to ignore the column numbers for the time and pressure data the time format and any desired thinn
22. s When both the theoretical solutions and data are plotted on a log log graph sliding the data vertically and horizontally is equivalent to adding or subtracting logarithms and thereby adjusting the constant term of the dimensionless parameters When a suitable match is obtained visually the parameters can be determined from the ratio of the real and theoretical parameters at any point on the graph This is equivalent to fitting a line except that curves are used and no assumption of linearity in the solution is required The adjust and compare method as implemented in PT is more direct in determining the parameters of the solution Instead of changing the problem into one of finding a straight line or matching some set of theoretical curves the data and theoretical solutions are plotted on the same graph and the parameters of the theoretical solution are adjusted until the best match is obtained Using this method we are able to analyze data which exhibit no straight line by any method as well as in situations where no set of type curves has been prepared The values of the parameters of the theoretical solution directly determine the desired analysis results PT User s Manual Page 23 Computation of Pressure Derivatives Although the technique is usually referred to as pressure derivatives the actual quantity used in pressure derivative analysis is the derivative of pressure with respect to the natural logarithm of time This correspon
23. se Once a project is created or opened the leftmost side of the PT main window shows the list of wells included in the project To the right of the wells a list of well tests is shown At the top of the window there are various menus and tool bar buttons as shown in the screen shot below 7 RESys PT Project Data Analysis Design Configure Language Help a2 8f c Project Test PT Project Wells PT Tests 1 30 2008 Storage Example Rosa amp Home SPE 22673 Table 1 30 2008 Sample DST Analysis First How Shutin Period 7 30 2008 Hamer Example Eadougher Monograph page 48 1 30 2008 Drawdown Example 1 Earlougher amp Kersch JPT Ju 1 30 2008 Example Buildup with Momentum 1 30 2008 Example South Texas Buildup Test 7 31 2008 Multi Rate w Buildup Eanougher Example 5 5 p 5 8 30 2008 Infinite Cond Fracture Gringarten et al SPE 5436 8 30 2008 Finite Conductivity Fracture Example Opening EXRESys NETXDataXTestP T mdb selecting any well in the list will display the list of well tests available for that well The menu at the top of the window allows access to the functions available in PT and includes functions to create and open projects wells and well tests etc The Toolbar contains buttons for rapid access to well test data and analysis functions such as viewing data entry various analysis methods etc The Project menu contains functions to create open and close projects and edit project information The
24. thm is always used in calculating pressure derivatives from actual data The scatter is reduced by using a higher order numerical method and by forcing time increments to be of a minimum magnitude thereby adding a smoothing effect to the derivative data The algorithm used is a second order Taylor s series approximation to the derivative with non evenly spaced points To derive the algorithm note that a Taylor s series approximation to subsequent data points can be written as dp Atz d p Diei Pit Aia rt 2 and dp Ati d p Pi 1 Di Ati T 2 di If we hypothesize a relation of the form dp a Ap At 41 Bp t Cp t Ati 1 PT User s Manual Page 24 we can substitute the relations from the Taylor series expansion for p t Ati 1 and p t Ati 1 to yield an expression for the derivative in terms of the adjacent function values and the constants A B and C By comparing the expression we require that the coefficients for all terms be zero except the coefficient of the first derivative term which should be 1 yielding 3 equations in A B and C By solving the three equations for the coefficients simultaneously a complete expression can be obtained Atf Ap pii Atf 1 Piri Pi At 4 Ati 1 Ati Atis1 In this formulation the second derivative error term vanishes so we have a formula that is more accurate but it is still susceptible to small errors in the data when At and Ati are small We get aro
25. total 6 7E 06 1 psia Viscosity 0 9 cp Well Examples PT 4lmport Test 77 30 2008 Storage Example Rosa Home Test 9 29 2010 Example 5 5 Gas well Drawdow PVT System PVT System Normal Gil e 5 3 Normal Oil Compressible Oil 0 85 i 0 87 0 0023 cp sco 0 01911 cp 45E 05 1 psia 0 000235 1 psia P pan Mu zy PT User s Manual Page 12 Test Analysis PT offers three main categories of well test analysis methids 1 Classical a Cartesian analysis for storage and reservoir limits b Semilog Horner and Miller Dyes Hutchinson methods c Square root of time for fractured well evaluation 2 Type Curves 3 Regression Any of the methods can be selected by choosing a well and a test then selecting the appropriate analysis method from the Analysis menu The following sections describe the various analysis methods in more detail Classical Cartesian Analysis q 4 v P d x Method Storage Well Examples Tet Storage Example Rosa Home SPE 22679 Table 1 m 1569 185 psia hr Pw 1 2999 361 psia hr Q Bbl D Results 0 00886607 bbl psia 8306 648 0 0 1 0 2 0 3 0 4 0 5 0 6 Time hr Points 4 0 63 2986 26 Std Dev 0 643 Cartesian analysis is a technique whereby the pressure vs time data is plotted on a Cartesian graph and a linear tendency of pressure with time is chosen Theory indicates that here are two main situations when a linear pressure vs time behavior would be expected 1 Early time
26. uid to be selected and the necessary fluid and rock property parameters to be entered In PT there are 4 types of fluid that can be selected For liquids either Normal Oil or Compressible Oil can be defined while for gases either an Ideal Gas or Real Gas fluid model can be selected The data needed for each case is shown in the displays below In most cases a Normal Oil will be used where the fluid is a slightly compressible liquid and the formation volume factor viscosity and rock compressibility are all that are needed For volatile liquids a Compressible Oil can be selected where a base pressure for the formation volume factor is specified as well as the fluid compressibility This model is rarely used and is only applies to fluid where the formation volume factor varies significantly during the test For gas well tests the choice of an Ideal Gas requires temperature z factor and viscosity information and will result in the use of P pressure squared analysis This is only valid for low pressure gases For most gas well evaluations the use of the Real Gas model is recommended but it also requires a table of viscosity and z factor versus pressure More information on the fluid models and the use of pSeudo pressure can be found in the Appendix PT User s Manual Page 11 Test 30 2008 Storage Example Rosa Home PVT System 3 Ideal Gas Normal Oil Real Gas Compressible Gil P Ba lg psia C oil lg 1 psia C
27. und that problem by placing a lower limit on the size of At and Atj 1 p x In effect we use a more accurate difference formula to minimize estimation errors but make the differences larger to ensure stability In pressure transient analysis instead of pressure derivatives we are actually interested in the semi log slope which is the derivative with respect to the logarithm of time The practical implication of that is the difference in t is replaced by the difference in log time Even though time differences may be large the logarithmic difference may be very small In practice we usually specify that the ratio of two times used in calculating the derivative are at least 10 20 different This has the effect of requiring that the At in the differentiation formula is on the order of 0 1 at the smallest and is usually adequate for most test data dp dp We also can take advantage of the fact that t d In t dt Applying this relation the formula normally used in calculating pressure derivative data is dp Ati 1 Ati p pii At Ati ua Pi d in t Ati Ati At Ati Ati Ati41 where t 4 lt 0 9 t and t1 gt 1 1 t PT User s Manual Page 25
28. w time before a shut in as in a drill stem test oquare root of time analysis can be done by selecting Analysis Classical Sqrt Time from the menu Type Curve Analysis Type curve analysis relies on the observation that the dimensionless parameters for time and pressure consist of reservoir and well parameters multiplied by time or pressure difference so the logarithms of the parameters are the logarithm of time or pressure plus the logarithm of the reservoir and well parameters When the theoretical pressure versus time response is PT User s Manual Page 15 graphed on a log log graph moving the data is the same as varying the pressure and time coefficients of the dimensionless parameters The coefficients are comprised of reservoir and well parameters allowing permeability estimation Type Curve Analysis al la Type Curve Radial Flow w Deri ei Li Well Examples Grid Test Storage Example Rosa Home SPE 22679 Table 1 V Derivatives Radial How with Wellbore Storage and Derivatives pD dpD d In tD Match Point tD 1 26 63561 pD 1 0 01508039 Results Rate 252 Bbl D kh 639 891 md4t k 9 27379 md 1000 10000 20 9885 10 8264 Type curve analysis can be done by selecting Analysis Type Curves from the menu A type curve set can be selected from the Type Curve drop down list Moving the mouse while pressing the left mouse button will move the data points relative to the curves Alternative
29. wellbore storage dominated flow The slope of the pressure change is PT User s Manual Page 13 proportional to the wellbore storage parameters 2 Late time semi steady state flow when the entire drainage area of the well is being depleted The slope of the pressure change is proportional to the drainage volume and compressibility Cartesian analysis can be done by selecting Analysis Classical Cartesian from the menu The parameters calculated can be determined by selecting the desired method from the Method drop down list Since well tests rarely last long enough to estimate reservoir volume Storage is the default method window will be opened displaying the graph of the pressure vs time data The user may select points fit a line to the selected points and compute either the wellbore storage or the reservoir drainage volume Classical Semilog Analysis Semilog Analysis c E Q A 4 v amp dh Method MDH Well Examples Test Storage Example Rosa Home SPE 22679 Table 1 m 78 2598 Pihr 2173 43 IblPrd Time Results kh 624 3685 mdt k 9 048819 md Skin 5 674597 dP Skin 386 3605 psia as i Rea i SEES dt hr Points 10 97 04 2827 2 Std Dev 0 391 semilog analysis methods rely on the observation that for radial transient flow the pressure changes linearly with the logarithm of time The most common analysis methods are 1 Miller Dyes Hutchinson MDH for wells with a single constant flow rate
30. will be added to that pseudo well Note that since PT4 did not explicitly store a test date all of the imported tests will have the current date which can be corrected by editing the test data To associate the tests with actual wells it may be necessary to create the wells as described above The tests can then be moved from the PT4Import well to the correct well by dragging the test onto the desired well with the mouse Entering Pressure Data Once a well test has been defined time and pressure data will normally be entered In PT there are two options 1 entering data manually or 2 importing data from a pressure gage data file To enter the data manually select the well and well test then select Data T P Data Edit from the menu A dialog will be displayed where the data can be typed in manually as shown below To accept and save the data press the Ok button FE P T Test Data Well Examples Tes 77 30 2008 Storage Example Rosa Home SPE Pw psia 29 4 In many common cases pressure transient data may be available in an Excel spreadsheet Note that the Excel data must be in 2 columns representing time in decimal hours and pressure To quickly copy time and pressure data from Excel to PT select the data in Excel and copy Cirl C then select the P T Test Data grid and press Ctrl V The data will be automatically pasted into the data entry form PT User s Manual Page 6 Importing Pressure Data In m
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