The choice of the optimal development method for low permeability reservoirs has been a major challenge for most oil companies in recent years.
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It is caused by the need to develop hard-to-recover reserves both in green fields and marginal zones of brown fields. Over the last 10 years the reservoir properties deterioration trend has led to the rapid advancement of technologies to drill horizontal wells with subsequent multi-stage hydraulic fracturing, and these technologies have started being widely applied to develop oil reservoirs in Russia. However, the traditional approach to the production technology – water flooding – still remains uncontested. It is not unusual that in the course of production of low-permeability reservoirs it becomes increasingly difficult to maintain the required reservoir pressure because of problems related to preparation of injection water: treatment to remove mechanical impurities and emulsions, selection of optimal salinity, etc. Without due preparation of the oil displacement agent wells injectivity may be greatly reduced resulting in low efficiency of both reservoir pressure maintenance and oil displacement efforts and the reservoir production system as a whole (low production rates, low recovery factor).
Capital investments required to drill injection wells and surface facilities (water intakes, water lines, pumping stations, etc.) have significant negative effect on economic efficiency of development projects. So it may be reasonable to consider alternative production options and models including natural drive, without a reservoir pressure maintenance system.
A vast experience in producing low permeability reservoirs by natural drive has been gained in North America at such fields as Bakken, Eagle Ford, etc. In view of this experience, this paper is discussing the issue of defining the critical parameters of the reservoir at which natural drive is more efficient than water flooding. An ideal situation is considered, taking no account of the above mentioned problems that may occur trying to maintain reservoir pressure in low-permeability reservoirs. An analytical model describing oil inflow to an MSHF horizontal well is constructed. Using this model key dimensionless quantities affecting the efficiency of production by water flooding and natural drive and the choice of the optimum well pattern is determined. The model run results are summarized in a master chart that allows looking at the key dimensionless quantities to define the optimal production method for an oil reservoir. This model also let to construct an analytical formula for the critical reservoir permeability value below which water flooding is less economical than natural drive production. This formula can be used for the critical permeability calculation for the Priobskoye field and there is a good convergence with the results of calculations by more complicated numerical models where injection wells work time was also optimized.
Об авторе:
Alexander Sitnikov, Deputy CEO, Geology and Petroleum Engineering, LLC Gazpromneft NTC
Graduated from Novosibirsk State University with the degree in Physics; then in 2005 he graduated from Tomsk Polytechnic University and Heriot-Watt University (Edinburgh, UK) with the degree in "Petroleum Engineering".
In 2005-2006 he worked in Sibneft in Well Screening and HFC Selection Team.
2006 to 2008: LLC Gazpromneft-East, Section Head, Stimulation and Well Technologies.
From 2008 to 2011, he worked as Deputy Head, Petroleum Engineering in Rosneft on the key fields of LLC RN-Yuganskneftegaz, i.e., Priobskoe, Malobalykskoe and Prirazlomnoe fields.
In 2012 he joined LLC Gazpromneft STC team as Deputy Director of Geology and Petroleum Engineering Department. He organized a full cycle of research and development support to Corporate projects and assets, participated in development of Gazprom Neft Technology Strategy in the area of geology and petroleum engineering.
Since 2014- Deputy CEO, Geology and Petroleum Engineering, LLC Gazpromneft STC.