Ahmad Reizky Azhar (754574) Henri Losoi (760256) Jiang Miaolun (762027)

Group 4

TPG4225 Fractured Reservoir Semester Project

� Project Background � Objective � Solving Method � Considerations � Result � Conclusion

Presentation Outline

Outline

�  Incorporate Warren and Root model of dual prorosity

Kazemi Model

Project Background

Figure 1. Idealization of a fractured system (from Warren and Root)

�  The model represent water wet reservoir with single matrix layer surrounded by fracture

Figure 2. Kazemi Model Eclipse Grid – Pressure Distribution

�  Two phase fluid flow in the fracture and matrix

�  Represent displacement of oil with water in naturally fractured reservoir with capillary dominated system

�  Incorporate matrix block saturated with oil which partially surrounded by another fluid which is gas at the upper part and water at the lower part

Sudation Model

Project Background

�  The invasion of fractures with gas will have an effect a downward advancement of gas-oil displacement front in matrix, while the water invasion in fractures will have as a consequence an upward advancement of water-oil contact.

�  Three phase fluid flow in the fracture and water wet matrix

�  Represent displacement of oil with both water and gas in naturally fractured reservoir with gravity drainage dominated system

Figure 3. Sudation Model Eclipse Grid – Pressure Distribution Figure 4. Sudation Model Eclipse Grid – Oil Saturation Distribution

�  See the effect of ignoring matrix capillary pressure in simulation of Kazemi model.

�  See the effect of different water injection rates in terms of: Ø  Recovery Ø  Well bottom hole pressure for producer and injector Ø  Water cut

in Kazemi model.

�  See the effect of ignoring gravity drainage in simulation of Sudation model.

�  See the effect of different gas injection rates in terms of recovery in Sudation model.

�  Describe the displacement mechanism for different production interval in Sudation model.

Objective

Main Task

�  Ignoring capillary pressure by changing matrix capillary pressure value to zero under SWFN section in Kazemi data file.

�  Do sensitivity of the water injection rates by changing fifth value under WCONINJE section in Kazemi data file.

�  Ignoring gravity drainage by comment out GRAVDR keyword by put two hyphens.

�  Do sensitivity of the gas injection rates by uncomment the line under WELSPECS, COMPDAT and WCONINJE section and changing the fifth value under WCONINJE section in Kazemi data file.

Simulation Using Eclipse 100

Solving Method

� Water injection sensitivity rate are 160, 170, 180, 200 and 210 STB/D.

�  Gas injection sensitivity rate are 1000, 2000 and 3000 MSCF/D.

Sensitivity Analyses

Considerations

� Compare effect of simulation with and without capillary pressure.

Figure 5. FOPT Simulation Result as the Effect of Capillary Pressure

Kazemi model

Result

Main Idea: Great difference between both cases

Kazemi model

Result

Figure 5 shows the performance of total field oil production for both case with capillary pressure mechanism and without capillary pressure mechanism. Black line represent cumulative oil production for case with capillary while red line represent cumulative oil production for case without capillary. In the first two months they are aligned which means production for both case is equal. This production comes from fracture where there is very high permeability in fracture compare to matrix resulting the oil from fracture will flow easily to producer. But after two months production, they are separated significantly where case with capillary pressure still following the same trend while case without capillary pressure trend is decreasing and keep producing in low rate until the end of simulation. This phenomena is caused by the effect of capillary forces mechanism.

�  In fluid statics Pc = Pnon-weting phase – Pwetting phase

�  When the driving forces is not very strong, �  Pc help oil prod à water wet �  Pc resist oil prod à oil wet

Theory Behind

Result

Kazemi model

Result

� Compare effect of different water injection rates.

Figure 7. FOPT Simulation Result as the Effect of Injection Rates

Main Idea: Q Inj < Q Inj crit Higher Q = higher FOPT Q Inj > Q Inj crit Higher Q = significantly fall FOPT

Kazemi model

Result

�  Figure 7 shows cumulative oil production for 5 different injection rate scenario. For the first 8 months, the production is align since this part is the contribution of fracture oil production. After 8 months production then water injection displacement is taking into account. The total recovery than will depends on water injection rate. There are 3 interval for water injection rates in naturally fractured reservoir model; low rates, critical rates and excessive rates. For low rates interval, the higher injection rate will improving recovery, until it reaches critical rate. It means the injection water will displace oil from matrix effectively. But after it exceed critical rate, water which has higher mobility than oil will just flowing through fracture where it has much more higher permeability and resist oil production from matrix by causing back pressure from fracture from matrix. After exceeding critical rate, then the higher injection rate will reduce cumulative production significantly. �  It indicated that 180 STB/D is the optimum injection rate while also the critical injection rate altogether.

Kazemi model

Result

� Compare effect of different water injection rates.

Figure 8. WBHP Simulation Result as the Effect of Injection Rates

Main Idea: 1. Align (small differences) BHP of I&P 2. Q Inj < Q Inj crit lower grid pressure (steeper pressure decline) Q Inj > Q Inj crit Higher grid pressure (smaller pressure decline even pressure is inclining for extreme case)

Kazemi model

Result

Figure 8 shows well bottom hole pressure of each set producer and injector for different case of injection rates. Clearly seen that there is not much different from bottom hole pressure of producer and injector at each case. It is because there is very high permeability in fracture that caused the pressure support from the injector directly transferred to producer with only small differences. This phenomena is unique where there is a fracture in the model. If there is only matrix exists in the model, pressure difference between injector and producer will be higher since matrix permeability is not as high as fracture permeability, causing high pressure drop from injector to producer.

Kazemi model

Result

Different injection rate will also resulted in different pressure distribution profile. As known that optimum injection rate is 180 STB/D injection rate, it is then become the optimum case which will give optimum pressure decline profile. For the cases where injection rate exceeding critical rate, bottom hole pressure distribution will be remain higher (small decline rate) while the cases where injection rate lower than critical rate will causing also lower bottom hole pressure (steeper decline) since the beginning of simulation. It means the higher the injection rates will give backpressure from fracture to matrix then resulted in higher pressure in the grid.

Kazemi model

Result

� Compare effect of different water injection rates.

Figure 9. WWCT Simulation Result as the Effect of Injection Rates

Main Idea: Higher Q Inj -  Higher total water cut -  Quick rising water cut

Kazemi model

Result

Figure 9 shows well water cut of each injection case. In the first ½ months they are very small and almost aligned caused by the existence of fracture. In this interval only oil from fracture is produced. After ½ months, they begin separated where the higher injection rates will increased water cut. It also aligned with previous explanation, when injection rates exceeding critical rate, it can cause back pressure from fracture while most of the oil from matrix is restricted to flow from matrix to fracture. Moreover, the significant different between fracture and matrix permeability is also supports this phenomena. Water will likely flow from fracture instead of imbibing matrix and displacing oil. When injection rates below critical rate, water will effectively support imbibition from fracture to matrix resulted in effective oil displacement by water in matrix,resulted higher oil and lower water cut. But since there is fracture exists in the model, it will lead to progressive increase of water cut regardless how much injection rates since mobility of water is higher than oil and fracture helps water to flow. The different between them is from the capability to displace matrix oil and produce oil from matrix.

Result

FGOR Analysis with the E100 Sudation Model Without/with Gravity Support �  Shape

�  Reservoir pressure above bubblepoint (BP), during BP and after BP �  First peak due to primary gas cap while second peak due to solution gas (segragation) �  Rapid acceleration in second peak due to high porosity/permeability values

�  Large height with the second peak �  More Slab so not surface (more capillary support) �  Large blocks (better storage)

�  Future research �  High densities: their effect on pressure support and flow? �  Large sigma: transmissive factor? (Look for Schlumberger Eclipse Technical Description manual)

Sudation model

Result

�  Figure 10 shows total gas oil ratio performance for both with and without gravity drainage simulation model. Black line represent gas oil ratio for the case with gravity drainage while red line represent gas oil ratio for the case without gravity drainage. For the first four years, they look alike where the gas production contribution mainly comes from dissolved gas in fracture oil which makes the gas production is gradually increasing. After 4 years, there are gas coning from gas cap resulted in significant rise of gas oil ratio for both cases. Since the limited amount of gas cap and quick pressure decline from gas cap, the gas oil ratio then fall again to lower level. After this point, the line will be separated. For the case with gravity drainage, there are gravity segregation occurs where the oil expand caused by dissolved gas coming out from solution. Due to density differences, dissolved gas then move to upper part then perform secondary gas cap. After new gas cap reaches its critical saturation, it then again make the gas coning into the producer. From this part, since gravity segregation is occurs for the whole reservoir which mostly matrix, the amount of dissolved gas coming out from the solution and produced become really high until it again reaches its peak performance, then it begin declining. For red line which is the case without gravity drainage, dissolved gas is not coming out from solution and resulted in lower gas produced since the amount of gas is not sufficient to make critical gas saturation.

Sudation model

Result

� Compare effect of different gas injection rates.

Figure 11. FOPR Simulation Result as the Effect of Injection Rates

Early time

Plateau time

Decline time

Main Idea: 1.  Not much

difference FOPR for different injection rate

2.  FOPR trend profile satisfy 3 unique interval

Sudation model

Result

� Figure 11 shows field oil production rate for different cases of gas injection rates. There are not significant difference of production rate performance from different injection rate. It because the amount of gas needed to displace oil from matrix is the same regardless of injection rates. All injection rates already fulfilled the minimum saturation. The excessive gas injected will directly flow to producer due to the significant different between gas and oil mobility where gas mobility is much higher than oil. Even in lower rate, due to the mobility difference gas will still easily breakthrough to producer.

Sudation model

Result

� Production of gravity drainage process will have three unique interval, which are early time, plateau and decline phase. For this simulation model, early time occurs in the first three years, plateau occurs in the next 4 years, and following by decline for the rest of simulation. In early time interval, production contribution mainly comes from fracture and few support from matrix. In the plateau time, production contribution mainly comes from matrix as the effect of gravity drainage mechanism. Since the oil in place mostly comes from matrix, so production at this interval is much higher and can be maintained in same rate. The last interval is decline where the oil saturation already low and also gas which coming out from solution already reach its critical saturation to flow, causing the dramatic rising of gas production which in the same time restrict oil to flow.

� Key observations �  Kazemi: 2 phase model (water-oil): Surface model �  Sudation: 3 phase model (water-oil-gas): Slab model �  High permeability/porosity values augment flow so aggressive changes �  Reservoir pressure above Bubble point, during BP and after BP

� Results due to geometries �  Pore size has significant impact on gas production suspected due to

capillary forces in slabs (Sudation) versus surface (Kazemi) as seen by GOR figure

�  Sudation (slab) more sensitive to gas injection �  Large blocks in Sudation attribute to increased segregation of solution

gas (second peak in FGOR) �  Oil production not sensitive to the geometries

Conclusion

Thank You