Study On Sedimentary Microfacies Of Tight Reservoir From Well Logs In Chang7of Yanchang Formation,Erdos Basin

With the rapid development of petroleum exploration and development, unconventional oil and gas resources has become the focus of global oil field. However, the exploration of tight oil reservoir is another hot area of the global unconventional oil and gas exploration and development following the successful development of shale gas on a large scale.Erdos basin is a typical lithological oil and gas reservoir, thus the development of sand body and physical conditions of reservoir are closely related to the deposition environment of sediments, that is to say the reservoir quality is controlled by the types of sedimentary facies, and dominant sand bodies develops in several typical sedimentary microfacies. But for now, sedimentary microfacies of chang7in Erdos basin are classified with different standards, the corresponding relationship between characters of logging curves and the microfacies is not clear, thus resulting in that the identification of extensive plane microfacies still can only rely on limited cored wells, greatly reducing the precision and the accuracy of the sedimentary microfacies.Different methods such as paleocurrent analysis, planar characteristic analysis of light and heavy mineral, detrital composition and content, plane characteristics of particle size are used to determine that the northeast and southwest are mainly the source direction in chang7period, and a variety of facies symbol in rock cores are used to conduct system partition of sedimentary facies types. Thereof, main sedimentary facies of chang7are Delta, sublacustrine fan and deep lake plains facies, of which delta front in study area is the most developed, which can be divided into two microfacies, underwater distributaries channel and distributaries bay;sublacustrine fan facies and deep lake plains are mainly developed in deep lakes, which include inner fan, middle fan and outer fan subfacies from the deep lake line to lake center; inner subfacies contain the main channel and overbank facies, middle fan subfacies include braided channel, channel, the center microfacies, outer fan subfacies include peripheral mat facies. Constrained by a large amount of core data, using density and gamma crossplot、volume cross section and gamma crossplot and various of overlapping map, such as gamma and gamma, to recognition sandstone、mudstone、oil shale and so on. This paper analyzes logging sedimentary microfacies relying on the aspects of conventional logging curve and imaging logging image feature. Based on the establishment of well logging facies symbols, establishing logging interpretation model of sedimentary microfacies, and analyzing different sedimentary microfacies sand body and reservoir control, it is determined that the main favorable sedimentary facies belts are subaqueous distributary channels in delta front and main channel in inner fan of sublacustrine fan.