Sedimentary Evolution And Its Petroleum Geological Significance Of Coal Measures Reservoir In Shanle Oilfield

Shanle oilfield is situated in the west of the Shanle tectonic belt, which is located in the northern piedmont zone of bruchfalten of the Turpan and Hami Basin. The oilfield is a coal measures reservoir oil field with special low porosity and low-permeability. The reserves size and the construction and production scale are expending year by year. However, because of the complicated geological structure of its principal producing formation, study of the depositional system and the sedimentary evolution patterns in the region of interest has not been carried out, and it greatly affect the exploration and development of the oilfield. By the study of the regional stratigraphic framework and depositional systems, this paper is aimed at awareness of the evolutionary pattern of depositional sequence and facies in the study area, accurate grasping sedimentary evolution model, clarifying its relationship with the oil and gas, in order to provide a reliable geological basis for the scheduling of the development program and the increasing of oil reserves and production.Based on analysis of the seismic data, well logging data et., combined with the characteristics of the regional tectonic and sedimentary evolution, this paper used the principles of high-resolution sequence stratigraphy, divided the Xishanyao formation and the Sangonghe formation into a third order sequence selective ly (long-term cycles) . On this basis, classified them into five 4th order sequences (medium-term cycles) . Through the well to seismic calibration, build up an isocdhronous stratigraphic framework of the Shanle oilfield. On the base of a comprehensive analysis of cores, flakes, sedimentary sequences, as well as logging, seismic and other similar signs, based on the basis of geographical location, the mobile system, such as a combination of factors, established the main sedimentary facies type of the Sangonghe and Xishanyao formations. There are there major kinds of sedimentary facies types developed in Xishanyao and Sangonghe formations, namely, lake, delta, fan delta.On the basis of the study of the regional stratigraphic framework and depositional systems, this paper proposed the sedimentary evolution model. Fan-delta depositional system developed in the increasing base level cycle of the Sangonghe third order sequence, and the semi-deep lake to deep-lake sedimentary system developed in the descending base level cycle. While delta to deep-water sedimentary systems developed in the increasing base level cycle of the Xishanyao third order sequence, and the shore-shallow lake sedimentary system developed in the descending base level cycle.Under the guide of the regional stratigraphic framework, this paper systematically analysed the sedimentary evolution of the study area, and established sedimentary evolution models of the oil fields Sangonghe formation and the Xishanyao formation in the Shanle oilfield. During the Sangonghe and Xishanyao formation deposition period, the study area has experienced four major sedimentary evolution stages: large-scale lake transgression phase of the Sangonghe, the lake basin-filling phase controlled by north-south bidirectional sources of the first segment of Xishanyao formation, the steady sedimentation phase of the second segment of the Xishanyao formation, and the lacustrine facies sedimentation phase of the third and fourth segments of the Xishanyao formation.Through the above study with the use of the geological and reservoir materials, this paper predicted the reservoir traps in the study area. The progradation delta facies sand body in the second fragment of the Xishanyao formation can form up dip pinch-out type reservoir; and deposits of the third and fourth fragments of the Xishanyao formation formed larger lacustrine turbidite sand body, they can form lenticular sand body lithologic traps.