Study On The Reservior Heterogeneity Of The Second Member Of Dainan Formation In Zhenwu Oilfield

Zhenwu Oilfield is located in the deep sag in the south of Gaoyou sag of Subei basin and is a complex fault block oilfield. Currently, Zhenwu Oilfield has been at the stage of high water-cut and it exposes many problems such as conspicuous differences among layers and the highly fragmented and complex distribution of remaining oil which increases the difficulty of the mining of remaining oil. The main reason is the serious reservoir heterogeneity. Given these, this article set the Second Member of Dainan Formation in Zhenwu Oilfield as the research object and analyzed the features of sedimentary microfacies of the study area, clarified the characteristics of the reservoir microscopic and macroscopic heterogeneity and has been clear about the influence of the reservoir heterogeneity on the distribution of remaining oil from various angles and by combining dynamic with static data. Several Achievements has been obtained as follows:(1)The Second Member of Dainan Formation in Zhenwu Oilfield is characterized by fan delta-oastal shallow lake deposition. E2d25-E2d23 sand group developed fan delta front and oastal shallow lake facies and underwater distributary channel and sand beach, sand bars microfacies are the most obvious; E2d22 sand group developed fan delta plain sedimentary, the main microfacies are distributary channel and distributary bay microfacies; To the sedimentary period of E2d21 sand group, the reservoir is characterized by fan delta front deposition with the water rising.(2)It points out that the Second Member of Dainan Formation in Zhenwu Oilfield has strong degree of microscopic heterogeneity: the rock and mineral heterogeneity is strong and compositional maturity and textural maturity of the reservior’s detrital component are low. The types of diagenesis are various: compaction is the most important diageneses which are destructive to the physical property of the reservoirs, however, dissolution and cementation have positive and negative influences on the physical property of the reservoirs. Pore distribution in the study area has strong heterogeneity: various types of pore structure and quantitative analysis of pore structure characteristics and it can be divided into four categories.(4) On the basis of the actual situation of reservoir, the method of data envelopment analysis was introduced to quantitatively characterize the reservoir heterogeneity. The characterized result shows that intrafomational and plane heterogeneity is moderate to strong and interformational heterogeneity is stronger; The heterogeneity of different sedimentary microfacies are different. According to the characterized result, this paper verifys the reliability of this method using the injection profile and fluid producing profile data which can be used to quantitatively characterize reservoir heterogeneity of the study area.(5) The control function of the reservoir heterogeneity on the distribution of remaining oil is definited from microscopic and macroscopic heterogeneity.The favorable areas of remaining oil are definited: the zone which has stronger pore structure heterogeneity, the layers with clear difference, the reservoir with more interlayers, the area with interformational stable layer, the zone which has poor reservoir physical property and whose heterogeneity index is between 0.5 and 0.9.