RESERVOIR SIMULATION USING MBAL (A CASE STUDY OF RZD FIELD.

RESERVOIR SIMULATION USING MBAL (A CASE STUDY OF RZD FIELD. 

    ABSTRACT

Fluid flow in a petroleum reservoir is a very complex phenomena and it is impossible to developanalytical solutions for practical issues due to the complex behaviour of multiphase flow.Reservoir simulation study the behaviour of fluid flow and provides numerical solutions tohydrodynamic problems of fluids in the petroleum reservoir-well systems with the help of asimulator. Reservoir simulation is used to predict the future performance of the reservoir so thatintelligent decision can be made to optimize the economic recovery of hydrocarbons from thereservoir. In this study MBal software was the simulator tool used. The study shows theapplication of MBal in predicting the future performance of the well. A work flow was applied forthis study and Data was gotten from RZD field and inputted to MBal, where result was gotten.MBal software calculation estimated STOIP as 149.184MMSTB, predict volume of the water influxas 47268.8MMft3, also show the effect of aquifer on the pressure of the reservoir and show thatwater drive is the predominant drive mechanism responsible for production. Also history matchingand prediction run was done and it was predicted that the reservoir was to have a life span of 33years with a recovery factor of 81.7%. This project show the importance of MBal in prediction offuture performance.

                                                    TABLE OF CONTENTS

CERTIFICATION .............................. i

DEDICATION ................................ ii

ACKNOWLEDGEMENT ................... iii

TABLE OF CONTENTS ................ iv

LIST OF FIGURES ......................... vi

LIST OF TABLES ........................ vii

LIST OF SYMBOLS ..................... viii

ABSTRACT .................................... 1       

CHAPTER ONE .......................... 2

INTRODUCTION ............... 2

  1.0 Brief Overview ................. 2

  1.1.  Background of Study ................. 2

  1.2.  Statement of Problem ............... 7

  1.3.  Aim and Objectives ................... 8

  1.4. Scope and Relevance ...................... 8       

CHAPTER TWO ............... 9

LITERATURE REVIEW .................. 9

  2.0 Introduction ...................... 9       

CHAPTER THREE ......................... 16

  METHODOLOGY .................. 16

  3.0 Introduction ................. 16

  3.1 Material Balance Evaluation and Analysis ............... 16

  3.2 Mathematical Concept of MBE Programmed Into MBAL ......... 18

  3.3 Analysis Of Various Drive Mechanism Using MBE ........... 21

  3.4 Step by Step Approach of Methodology ........... 24       

CHAPTER FOUR ............. 29

DATA PRESENTATION, RESULT AND DISCUSSION ............ 29

  4.0 Description Of Tool (MBal) Used In These Study ............. 29

  4.1 Data Presentation ................ 29

  4.2 Result and Discussion .................. 32       

CHAPTER FIVE ...........................37

   CONCLUSION AND RECOMMENDATION .........

REFERENCE ...................... 39

APPENDICES ................. 42

                                 LIST OF FIGURES

Fig 1.1   Showing the diagram for conservation of mass……………..3

Fig 3.1   Work flow for MBal………………………………………….17

Fig 3.2   Input Screen in MBal………………………………….27

Fig 4.1   Start up menu of Material balance (MBal)……………………………30

Fig 4.2   Aquifer plot………………………....33

Fig 4.3  Graphical plot showing the STOIIP……………..33

Fig 4.4   Analytical Plot (Aquifer Performance)………….34

Fig 4.5   Energy showing the Active Drive Mechanism………………34

Fig 4.6   Production simulation for Tank pressure vs Time………..35

Fig 4.7   Production prediction for Tank Pressure vs Time……..35

Fig A1    Matching Correlation in MBal 1………..45

Fig A2    Matching Correlation in MBal 2…………….45

                                   LIST OF TABLES

Table 1.1   Data required for MBE………………4

Table 3.1   Havlena and Odeh straight line MBal Derivations………….20

Table 4.1   PVT data for RZD Field………………..32

Table 4.2   Tank parameter…………………….32

Table 4.3   Water Influx Data……………….32

Table 4.4   Relative Permeability Data…………….31

Table 4.5   Production data for RZD Field…………….31

Table 4.6   Showing the summary of the RZD field analysis result…………….32

Table 4.7   Summary of input for the Aquifer model of MBal………32

Table A1    Production generated by MBal……………….42

                                 LIST OF SYMBOLS

Symbols                   Definition

A                            Reservoir Area Acres

Bg, Bo, Bw            Gas, oil and water Formation Volume Factor

Bgi, Boi, Bwi         Initial Gas, oil and water Formation Volume Factor Oil

Cf, Cw, C, C        Formation, water, Total and oil Isothermal Compressibility Factor

        to

dv                            Change in volume

dp                            Change in pressure

ΔNp                        Oil Production from pressure interval pn-1 to pn

Δp                           Change in Average Reservoir Pressure

E, E, E               Oil and dissolved gas, Gas cap gas and Connate and rock Expansion

ogf,w

F                              Total underground withdrawal

Gp, Np, Wp            Cumulative Gas, oil and water Produced

h & k                       Reservoir thickness & permeability

K, K                    Relative gas and Oil Permeability

rgro

m                             Gas cap size

P, P                        Initial Pressure and pressure

i     

N                             Stock oil initial in place

R                               Cumulative produced gas oil ratio

p

Rsi & Rs                 Initial Solution & Solution Gas Oil Ratio

Sg, So & Sw           Gas, Oil & Water Saturation (function of pressure and/or time)

Swi                          Initial Water Saturation v/v

Ug & Uo                 Gas & Oil Viscosity

We                          Water Influx into Reservoir

GBW            Gas, formation volume factor and water Injection

inj,inj,inj  

                  CHAPTER ONE:   INTRODUCTION 1.0:  A Brief Overview;  A  petroleum  reservoir  is  an  underground  porous  and  permeable  rock  medium  that  contains naturally accumulation of producible hydrocarbon, which are confined by impermeable rock and sometimes by water barriers. Fluid flow in such a porous medium is a very complex phenomena. Generally,  analytical  solutions  to  mathematical  models  are  only  obtainable  after  making simplifying assumptions in regard to the reservoir geometry, properties and boundary conditions. However, such simplifications are often invalid for most fluid flow problems. In many cases, it is impossible  to  develop  analytical  solutions  for  practical  issues  due  to  the complex  behaviors  of multiphase  flow,  nonlinearity  of  the  governing  equations,  and  the  heterogeneity  and  irregular shape of a reservoir system. As a result, these models must be solved with numerical methods such as finite difference or finite element. Reservoir Simulation is an area of reservoir engineering in which computer models are used to predict the flow of fluids (typically, oil, water, and gas) through porous media (Okotie 2015). Reservoir simulation provides numerical solutions to hydrodynamic problems  of  fluids  (oil,  gas  and  water)  in  petroleum  reservoir-well  systems  with  the  help  of  a simulator.  Today,  it  has  become  a  standard  tool  in  petroleum  engineering  discipline  and  been widely used for solving a variety of fluid flow problems involved in recovery of oil and gas from the porous media of reservoirs.     

1.1. Background of Study:  Reservoir  Simulation  is  the  process  of  mimicking  or  inferring  the  behavior  of  fluid  flow  in  a petroleum reservoir system through the use of either physical or mathematical models (chevron 2006). The process of reservoir simulation to predict the performance of a petroleum  reservoir continues  throughout  the  life of the  field,  meaning  performance  prediction  is  updated  over the producing  life  of  the  reservoir  as  more  data  becomes  available.  The  application  of  reservoir simulation is to predict future performance of the reservoirs so that intelligent decisions can be made to optimize the economic recovery of hydrocarbons from the reservoir. Reservoir simulation can also be used to obtain insights into the dynamic behavior of a recovery process or mechanism.  Reservoir simulation make use of tools (SIMULATOR) to carry out these process. In this study, MBal software will be the simulator tool to be used. MBAL is a simulation tool made up of various tools designed to help the engineer to gain a better understanding  of  reservoir behavior  and  perform  prediction  run.  The various  tools  available in MBAL are (MBAL user manual, 2005);   

 Material Balance   

 Reservoir Allocation   

 Monte Carlo Volumetric   

 Decline Curve Analysis,   

 1-D Model (Buckley-Leverett) and   

 Multi-layer The tool to be used in MBAL for this project is material balance.     

1.1.1 Material Balance: Material Balance equation is based on the application of the equation of conservation of mass to petroleum reservoir for the purpose of making quantitative deduction.                                                                                                      IN                                                                 OUT                                                                                                            IN – OUT = ACCUMULATION  Fig 1.1: Showing the diagram for conservation of mass   IN – Amount of fluids present in the reservoir initially (vol)   OUT – Amount of fluids produced (vol)   ACCUMULATION – Amount of fluids remaining in the reservoir finally (vol)                                              It was developed by Schilthius in 1936, it covers area that contributes to the pressure production history.  Material  balance uses  actual  reservoir  performance  data  and  therefore  is  generally  accepted  as  the  most  accurate  procedure  for  estimating  original  oil  and  gas  in  place.  It  is  the reservoir engineer’s basic tool for interpreting and predicting reservoir performance. The material balance uses a model that is existing as an imagination of the reservoir to actually tell or forecast the behaviour of the reservoir established on the effects of production of fluid from the oil pool and injection of gas and water. The material balance equation is considered to be a tank model which implies that there is no time parameter in the area produced. The ways at which the wells are drilled into the reservoir are positioned and oriented alongside with the dynamic effects of fluid which are not considered, hence the heterogeneous nature of the reservoir do not reflect, but it is still being used by Reservoir Engineers as a tool for interpreting and predicting reservoir performance. In the cause of this study, to illustrate the method, only sections specifically dealing with the material balance principles are included. Additional geologic information and basic data are reported to better acquire an understanding of the cases and thus to better follow the reasoning that suggested the successful application of the straight-line method of solving the MBE. Table 1.1 Data required for MBE Data  Source PVT Data  From PVT reports, correlations Production data  Well and reservoir records Ratio of gas cap volume to oil volume From wireline log, reservoir modeling (M) Oil and gas in place   From volumetric estimate and geological model Connate water saturation  From petrophysics (core and log) Water compressibility  From correlation or measured Pore compressibility  From correlation or measured  Reservoir pressures  From pressure survey Water influx  Calculation or history  The accuracy of material balance is based on the consistency of results when applied at successive intervals and agreement of the Material balance equation (MBE) result with result gotten from volumetric technique.    It is applied at later stage of development (after 20% of initial oil/gas is produced, or 10% of initial reservoir  pressure  has  declined).  It  uses  the  reservoir  pressure  measurements  to  determine estimates of oil in place and gas in place, and develop an understanding of the reservoir’s drive mechanisms. The Material balance equation relies on the assumption that as oil, gas and water are produced from the reservoir; there will be corresponding change in the reservoir pressure and the expansion of oil, gas, water, and rock.  The Material Balance procedure describes the expansion of oil, gas, water, and rock over time as a pool is produced. When fluid is removed from a reservoir, reservoir pressure tends to decrease and  the  remaining  fluids  expand  to  fill  the  original  space.  Injection  situations,  such  as  water flooding or gas storage, are handled by treating the injection volumes as negative production. The material balance equation may be expressed in a number of different forms and the general form  of the equation  applies  to  a  reservoir containing  a  gas  cap,  gas  saturated  oil  and  connate water, producing under a combination of primary drive mechanisms. The estimate of STOIIP for a saturated reservoir is stated below as:                 DD+D−DD+DD−D  D=… … … … … … … … … … … (1.1)                       D                                  D(1 +D)      D−D+DD− 1+DD+D∆D                      D1 −D                                                                                                                                  Its application prior to a 3D numerical simulation can provide a valuable insight that would guide in  proper  initialization,  history  matching  and  production  forecast  of  the  reservoir  thereby increasing confidence in the obtained results.  In  the  cause  of  this  study,  to  illustrate  the  method,  only  sections  specifically  dealing  with  the material  balance  principles  are  included.  Additional  geologic  information  and  basic  data  are reported to better acquire an understanding of the cases and thus to better follow the reasoning that suggested the successful application of the straight-line method of solving the MBE.     

1.1.2 Relevance of Material Balance:  Material Balance are used to estimate hydrocarbons in place (OIIP and OGIP) from measurements of fluid production and the resultant  change in reservoir pressure  caused  by that production.  It comprises of powerful simulation packages. It is one of the most efficient models suggested as a   RESERVOIR SIMULATION USING MBAL (A CASE STUDY OF RZD FIELD 5  necessary step prior to carrying out a simulation study; an integral part of reservoir simulation and modeling and optimization studies in successful reservoir management. While it is unrealistic to expect unique results under all conditions, material balance will always identify the reasonable bounds of the following parameters:    Initial hydrocarbon volumes in place    Water influx    Reservoir pressure    Future reservoir performance    Ultimate hydrocarbon recovery under various type of primary drive mechanisms. One of such simulation package using the material balance model is the one that will be used in this  research,  is  called  MBAL.  Just  as  the  material  balance  equation,  all  the  assumptions  are imbedded into the simulator. It is a package licensed in the Integrated Production Management (IPM) Toolkits, a property of Petroleum Expert Limited. A detailed process of it will be presented in chapter three of this work.       

1.1.3 Basic Material Balance Assumptions:   Some of the assumptions employed in the material balance equation are:     Reservoir is considered to be a single tank.     Pressure, temperature, rock and fluid properties are not space dependent.     Thermodynamic equilibrium always attained.    Production data are reliable.             

1.2. Statement of Problem:   The concept developed in MBal make use of material balance which has some limitations. Thus, in simulating an hydrocarbon reservoir with this concept there are inherent problems associated with it such as; The knowledge of the geologic trend is lacking It does not account for wells drilled in the reservoir It makes use of average properties that is it does not account for lateral and vertical variation in properties in reservoir fluids (oil and gas). Matching of PVT data with data gotten from the laboratory It  can  only  apply  to  reservoir  that  have  sufficient  pressure  and  pressure  history.  (producing reservoir) that is it is not applicable to virgin or newly producing reservoir as a rule of thumb not applicable for reservoir less than 6 months due to uneven distribution of pressure transient in the reservoir. (PNG 410) Highly sensitive to pressure measurement.  The accurate determination of oil and gas initially in place and the prediction of the future reservoir performance  are  of  vital  importance  to  the  oil  and  gas  industry,  also  an  accurate  and  reliable production data directly impacts the accuracy of the estimate and future performance. Thus,  material  balance  equation  method  unlike  volumetric  can  predict  future  reservoir performance and calculate water influx using Material Balance (MBAL) Model.  In practice, the material balance calculation is quite complex and its application requires several simplifying assumptions, including: A constant reservoir temperature is assumed despite changes in reservoir pressure and volume.  With  the  use  of  simulator  such  as MBAL,  we  will  be  able  to  predict  the  performance  of  the reservoir and recommend best operational production schemes to maximize economic recovery.         

1.3. Aim and Objectives:  The aim of this project is to apply a material balance model to predict future performance of the well, with the Objectives of:    Estimating STOIIP     Detecting if there is aquifer present in the reservoir and if there is, what is the strength of     the aquifer    Predict the future performance of the reservoir And finally, from the result, determine the best operational production scheme that would economic maximize recovery.       

1.4. Scope and Relevance:    This  project  work  is  basically  on  prediction  of  oil  reservoir  performance  and  analysis  using Material Balance Model in the “MBAL” Software, making use of the available data from a RZD Field Reservoir.  On the contrary, there are other methods of reservoir prediction tools but are not accounted for in the course of this study. Moreover, it should be noted that there is nothing inherent in MBAL that makes feasible all the time; rather its reliability is a direct function of the available data and the competence and integrity of the analyzer (Reservoir Engineer).  The  relevance  of  this  study  is  to  effectively  use  MBAL to  predict  the  RZD  Field  reservoir performance and recommend an economic recovery strategy as an implied production optimizer.