DIFFERENTIAL PETROLEUM CHARGING CONTROLLED BY ACTIVITIES OF TWO CONJUGATE STRIKE-SLIP FAULTS IN SHUNBEI AREA, TARIM BASIN, NORTHWEST CHINA

Recently considerable hydrocarbon reserves have been discovered in two conjugate strike-slip fault zones in Shunbei oilfield in Tarim basin. Through the integrated analysis of crude oil physical properties and geochemical compositions and fluid inclusion petrographical characteristics and homogenization temperature, the thermal maturity and petroleum charging history of Shunbei oilfield have been investigated. Analysis of the petrographical characteristics and homogenization temperature of oil and coeval aqueous inclusions in the two Fault zones revealed differential petroleum charging histories since the Early Yanshan around 200Ma. For SB5 Fault zone, two discrete ranges of homogenization temperature of coeval aqueous inclusions indicate an intense charging during Early Yanshan around 200Ma to 150Ma, and a minor charging during Late Himalayan around 20 Ma to 10 Ma. For SB1 Fault zone, the prolonged homogenization temperature range probably reflect a continuous charging from Early Yanshan to Late Himalayan around 10Ma. In addition, the presence of bitumen/bitumen inclusions and their associated high equivalent Ro values indicate a speculated earliest petroleum charging event during the late Caledonian, which might have been destroyed later by Permian igneous activities. Differential petroleum charging during Himalayan most likely caused stark differences in thermal maturity of crude oil and trapped oil and mixing of oils with variable maturity, with SB1 Fault zone receiving more intense charging of late-stage generated oils than SB5 Fault zone, evidenced by discrepancies in physical properties, fluorescence color and homogenization temperature ranges of fluid inclusions, and MPI-1 values. The late-stage differential petroleum charging during Himalayan can be explained by preferential reactivation of NE trending strike-slip faults, which was ultimately controlled by the regional NE 45° oriented compressive stress field. Crude oil with high maturity would preferentially migrate vertically via reactivated NE striking SB1 Fault zone, and charged into carbonate reservoirs, resulting in the current maturity differences in crude oils and trapped oils in Shunbei oilfield. The analysis of differential petroleum charging history in Shunbei oilfield not only is of great importance to deepen the understanding of regional petroleum accumulation mechanism, but also can serve as analogue for analyzing deeply-buried petroleum systems in similar strike-slip fault zones.