Carbonate reservoirs differ significantly from their sandstone counterparts and as such require alternative reservoir engineering approaches. Improvement of efficiency of development of carbonate reservoirs with as a rule low recovery factors has become the hottest topic for researches and operators. Tatneft PJSC has performed dedicated flow-after-flow tests, which involved 36 injection wells in carbonate reservoirs to improve understanding of fluid flow in carbonate rocks. The resultant long-term pressure and rate data defy description by linear flow models. Having analyzed nonlinear flow models, we decided on a model with an exponential relationship between the transmissibility and the pressure, which yielded a high description accuracy of inflow performance relationship (IPR) curves and acceptable accuracy of long-term pressure and rate data. The obtained pressure exponential coefficient of transmissibility exceeded by an order the deformation coefficient that accounts for the exponential change of permeability in core flooding experiments. This can possibly be explained by additional account for variations in the net thickness and the effective viscosity of the displaced oil vs. variations in pressure. A high per cent (94%) of smooth IPR curves suggests that increase of injection pressure results in gradual reopening of the existing fractures, both natural and induced, rather than creation of new ones, which has been a common belief. It was found that the conventional interpretation of drawdown curves using linear flow models yields multiple overestimations of fractures’ lengths in carbonate rocks (underestimation of geothermal skin factor). A reliable fracture length cannot be determined unless injection curve(s) and the flow model accounting for conductivity vs. pressure are additionally used. The obtained relationships will be used as input data for future model studies to improve our knowledge of carbonate rocks and to enhance the efficiency of waterflooded development of hydrocarbon assets in carbonate reservoirs.
References
1. Bakirov A.I., Sovershenstvovanie tekhnologii izvlecheniya nefti zavodneniem iz karbonatnykh kollektorov mestorozhdeniy Tatarstana (Improving the technology of oil recovery by waterflooding from carbonate reservoirs of Tatarstan fields): thesis of candidate of technical science, Bugul'ma, 2018.
2. Molokovich Yu.M., Markov A.I., Suleymanov E.I. et al., Vyrabotka treshchinovato-poristogo kollektora nestatsionarnym drenirovaniem (Development of a fractured-porous reservoir by non-stationary drainage), Kazan': Regent" Publ., 2000, 156 p.
3. Diyashev R.N., Sovmestnaya razrabotka neftyanykh plastov (Joint development of oil reservoirs), Moscow: Nedra Publ., 1984, 208 p.
4. Khabibrakhmanov A.G., Zaripov A.T., Khakimzyanov I.N. et al., Otsenka effektivnosti uplotneniya setki skvazhin na nizkopronitsaemykh karbonatnykh kollektorakh (na primere mestorozhdeniy Respubliki Tatarstan) (Evaluation of the efficiency of compaction of a grid of wells in low-permeability carbonate reservoirs (on the example of fields in the Republic of Tatarstan)), Kazan: Slovo Publ., 2017, 199 p.
5. Nugaybekov R.A., Shafigullin R.I., Kaptelinin O.V. et al., Evaluation of flooding system performance on oil deposits in carbonate reservoirs of Novo-Yelkhovskoe oil field (In Russ.), Problemy sbora, podgotovki i transporta nefti i nefteproduktov, 2011, no. 3, pp. 94-97.
6. Mukanov A.R., Bigeldiyev A., Batu A., Kuvanyshev A.M., Features of field development with tight carbonate reservoirs by waterflooding, SPE-202534-MS, 2020, DOI: https://doi.org/10.2118/202534-MS
7. Ligin'kova Ya.S., Issledovanie osobennostey zavodneniya zalezhey nefti v karbonatnykh kollektorakh (na primere Gagarinskogo i Opalikhinskogo mestorozhdeniy) (Investigation of the features of waterflooding of oil deposits in carbonate reservoirs (on the example of the Gagarinskoye and Opalikhinskoye fields)), Collected papres “Problemy razrabotki mestorozhdeniy uglevodorodnykh i rudnykh poleznykh iskopaemykh” (Problems of development of deposits of hydrocarbon and ore minerals), Proceedings of XII All-Russian scientific and technical conference, Perm: Publ. of PSTU, 2019, pp. 43–45.
8. Iktisanov V.A., Bobb I.F., Ganiev B.G., Study of the problem of optimization of bottomhole pressure for fractured-porous reservoirs (In Russ.), Neftyanoe khozyaystvo = Oil Industry, Neftyanoe khozyaystvo, 2017, no. 10, pp. 94–97, DOI: 10.24887/0028-2448-2017-10-94-97
9. Iktisanov V.A., Smotrikov N.A., Baygushev A.V. et al., Injection wells’ limited bottomhole pressures in carbonate reservoirs (In Russ.), Neftyanoe khozyaystvo = Oil Industry, Neftyanoe khozyaystvo, 2021, no. 12, pp. 94–97, DOI: 10.24887/0028-2448-2022-1-70-73
10. Iktisanov V.A., A method for evaluation of the effectiveness of injection wells operation (In Russ.), Neftepromyslovoe delo, 2020, no. 1, pp. 32–35, DOI: 10.30713/0207-2351-2020-1(613)-32-35
11. Iktisanov V.A., Opredelenie fil'tratsionnykh parametrov plastov i reologicheskikh svoystv dispersnykh sistem pri razrabotke neftyanykh mestorozhdeniy (Determination of filtration parameters of reservoirs and rheological properties of disperse systems in the development of oil fields), Moscow: Publ. of VNIIOENG, 2001, 212 p.
12. Gorbunov A.T., Razrabotka anomal'nykh neftyanykh mestorozhdeniy (Development of abnormal oil fields), Moscow: Nedra Publ., 1981, 237 p.
13. Dobrynin V.M., Deformatsii i izmeneniya fizicheskikh svoystv kollektorov nefti i gaza (Deformations and changes in the physical properties of oil and gas collectors), Moscow: Nedra Publ., 1970, 237 p.
