The Formation And Distribution Of Remaining Oil At Extra High Water-cut Stage

The first formation of lower part Es3 in Zhuang-52 fault block of Wuhaozhuang oil fieldis characterized by an average porosity of 19.37%, permeability of 183.12×10-3μm2, thewater cut up to 94.2%, low recovery of only 19.8% and still considerable remaining oilpotential. The main problems at present are the imprecise study on geological features, invalidcycles caused by channeling pathway, unawareness of the form and distribution for remainingoil. Therefore, we carried a research on the form and distribution of remaining oil during thehigh water cut in the first formation of lower part Es3 in Zhuang-52 fault block ofWuhaozhuang oil field, which can give a beneficial guide and of practical values forremaining oil finding and recovery rate in old oil field.With the application of modern reservoir description technique and a full use of theavailable data ,such as the geological information, logging data, seismic data, well andproduction testing and production performance information, an analysis of the origin for theregional structure was done at first; On this basis, we started from the regional structure originanalysis and determined the faults spatial development and distribution; Then we studied themicro-structure developed in the reservoir and found the micro-structure pattern; by way of aninvestigation of the rock-electricity and facies-electricity relations and the dividing of thesedimentary micro-facies on every monolayer basis in single well, the basic patterns for thefacies in both profile and plane were concluded; Finally, the logging reservoir evaluation workcan be carried, and a series of reservoir parameters were calculated for a purpose of thereservoir heterogeneity study in inner-layer, inter-layer and plane, which can also lay a betterfoundation for the final study of the remaining oil. In this paper we applied the new SNP-1, PND-S logging techniques to identify remainingoil saturation in single well. On this basis, we made an analysis on the controlling factors anddistribution rules of remaining oil within inter-layer and inner-layer in single well. Using thesaturation and relative permeability data derived from core analysis, we regressed to thepractical formula for remaining oil saturation. Then we calculated the remaining oil saturationin the whole region. At last, the characteristic of remaining oil distribution in plane was studiedby integrated analysis of horizontal heterogeneity and reservoir channeling-path.Under a full use of static and dynamic information and an analysis on the controllingfactors toward the remaining oil,we made a study on the remaining oil distribution pattern inboth plain and section. In plain, the non-main facies belt showed a relative abundance inremaining oil as a result of a relative poor water drive effectiveness whereas the main faciesbelt could also not ignore for potential further taping by virtue of its considerable primaryconserve. The corner zone of the main facies belt can suffer a relative poor water drive, and atthe same time the bypassed area within injecting wells and the place adjacent to low gradefaults can also be the target tapping area for the remaining oil. In section, the third sub-layerbears better displacement efficiency than other sub-layers because of strong interlayerheterogeneity and the second and forth sub-layer may have an relative remaining oilenrichment. Besides, positive rhythm thick layers can find a remaining oil concentration in theupper part and the remaining oil can also be abundant in section with a high interlayeroccurrence. So in this region, we concluded six models for remaining oil distribution, they arewidespread distribution of differential oil layer, injection imperfect type, by-passed zone type,interlayer interference type, inner-layer un-flooding type, low-order fault seal type, and wegave comprehensive evaluation to the potential oil ,which can provided definitely target forexploitation.According to types of remaining oil distribution and distribution mode, correspondingtechnical measures and rearrangement direction are established. Development Strategies areproposed as follows: synthesizing regulation to sub-well; a well network with partly selectivemining; continuation of water injection; a small amount of new wells drilled to improve theinjection-production system by restoration old well-based; Different Procedure measures,suchas filling and sealing holes with cards, extracting liquid, unstable water injection should be adopted in order to improve production results according to types of residual oil. Part ofthese measures have been implemented and good potential tapping result has been achieved.