Research On Seepage Theory And Use Of Petroleum Reservoir Engineering Of Sand-conglomerate Reservoir Formation In Mobei Oilfield, Xinjiang

It has been predicted that more than ten millions reserves was found in Mobei oilfield of Xinjiang in October,2010, about millions of which would be developed. And dute to that, Mobei oilfield has became one of the biggest of large piece thin reservoir with the development of rolling mode for the past few years. But the problems, such as, misunderstanding of the waterflooding mechanism, shortness of water free production period, deliverability descend hasty when water breakthrough, the low final recovery efficiency and so on, were widespread in the process of development of the old oilfield blocks. In order to insure the compilation of the development plan and the efficient development of Mo 116 well field, some critical technologies, including constant speed mercury injection, NMR, Multi-functional seepage platform and numerical simulation calculation, were applied to study physical characteristic of sand-conglomerate reservoir, percolation mechanism, effective displacement theory and pattern well spacing and so on. We also evaluated the performance of old oil field blocks. Main results are as follows:(1) It has been evaluated systematacially the properties of sand-conglomerate reservoir and demonstrated that the parameters of microscopic pore structure characteristics, mobile fluid saturation and trigger pressure gradient have the very good corresponding relation with reservoirs lithologies.(2) We also found out the characteristics of micro pore structure of Mobei oilfield. And we thought that the size and distribution of the throats was critical factor to determine the flowing capacity and development of the reservoir. Base on of micro pore structure, we have built flowing theory model, which could predict the reservoir production dynamic performance.(3) Compared with other low permeability reservoir, the reason why it’s easy to inject water and the water displacement efficiency is low in Mo 116 well field is that the mainstream throat radius of Mobei field is wider, the trigger pressure gradient is lower and the microscopic heterogeneity is more serious.(4) The reservoir of Mobei field has some degree of sensitivity, including weak speed sensitivity, weak pressure sensitivity and medium water sensitivity. There has been high bound water saturation and its common seepage interval is very narrow, only 20%. Althought breakthrough recovery reach up to about 85%, it’s hard to increase production when water breakthrough because water content will rise to 90% quickly. In the process of development, there exists some degree ability of imbibition oil recovery.(5) Base on the equivalent seepage theory, we have obtained the model of three districts, two-phase theory of seepage of water flooding which considered the trigger pressure gradient. We also demonstrated the influencing factors of water injectiom effectiveness, and gave theoretical chart boards about rationale well nets spacing and effective water injection.Applying the above results to actual oilfield development, there are two ways to improve the final recovery efficiency of Mo 116 well field. The first one is to optimise well network, well spacing and production system to prolong the water free recovery. The second one is to ameliorate water-injecting profile in the later stage of waterflooding, which could improve spread coefficient and brought higher recovery efficiency.