Study On Lower Paleogene Sequence Stratigraphy In Chaluhe Fault Depression Of Yitong Fault Trough And Non-structural Trap Prediction

Chaluhe fault Depression located in the middle of Jilin province, with an area of 1350km~2, is the largest structural unit of Yitong Fault Trough, extends northeast.Guided by sequence stratigraphy and modern sedimentology, efficiently utilizing geophysical data, drill core, well log, test and analysis data, this paper summarizes depositional systems, recognition marks of stratic surface and partition standards of sequence stratigraphic unit, sets up equivalent time micro-strata framework, divide the paleogene of the study area into 1 megasequence, 6 supersequence, 12 third-order sequence, and 36 tracts, and assured the sequence stratigraphy interface and traditional lamination interfacial parallelism relation: sequence 01 to the first part of Shuangyang, sequence 02 to the second part of Shuangyang, sequence 1 to the third part of Shuangyang, sequence 2 to the first part of Sheling, sequence 3 to the second part of Sheling, sequence 4 to the first part of Yongji, sequence 5 to the second part of Yongji, sequence 6 to the third part of Yongji, sequence 7 to the fourth part of Yongji , sequence 8 to the first part of Wanchang, sequence 9 to the second part of Wanchang, sequence 10 to the third part of Wanchang. sequence 01-02 Constitute the first supersequence, sequence 1-3 Constitute the second supersequence, sequence 4-6 Constitute the third supersequence, sequence 4 Constitute the fourth supersequence, sequence 8-10 Constitute the fifth supersequence, Qijia strata under the sequence 10 Constitute the sixth supersequence.In different basin evolution phase, with different structural settings and different sediments supplies, study area develops eight sequence patterns: shallow lake I-sequence, braided delta I-sequences, scalloped delta I-sequence, deep lake I-sequence, alluvial I-sequence, coal-bearing I-sequence, river I-sequence, riverbank I-sequence;and Liangjia fault bench slope-break pattern, Wanchang adjusting sedimentary slope-break pattern and, Botai deep slope-break pattern.Lake surface changing curve in study area have the similar trend with that of the secondary cycle of international sea raise and fall level, but the largest flood time lags behind that of sea;lake surface changing curve is substantially coupled with that of C and O isotope, reflecting that third-order sequence is controlled by lake surface change in the study area.After extending sedimentary systems of 10 sequence of highstand systems tracts and lowstand systems tracts separately which is 20 equivalent time units, statistically analysis combining sequence stratigraphy with oil and gas bearing relationship, it shows that: sequence4,5,6 are most favorable oil and gas bearing sequence, lowstand systems tract is non-structural trap where oil and gas accumulate;incise valley shaped during low water level period, as well as turbidity fan and scalloped delta systems developed during transgression and high water level period, can form lithologic, over nipped, fault and semi anticline, unconformity screened or compound trap reservoirs.In the study area Liangjia fault bench slope-break, Wanchang adjusting sedimentary slope-break and Botai deep slope-break have great controlling affects to sedimentary sand and traps. Lowstand systems tract developed area controlled by Wanchang outskirt slope and Liangjia secondary slope-break, turbidity fans and Botai depressed slope zone whose provenance came from north and north-northeast, are favorable places for the development of non-structural traps.