Abstract
The foreland slope in the south marginal Junggar Basin (SMJB) is geologically favorable for mass lithologic oil and gas reservoir accumulation. Based on outcrops, thin sections, individual-well facies, and cross-well stratigraphic correlation, the stratigraphic distribution and features of the Upper Jurassic Kalazha Formation were investigated in the SMJB. There are two sedimentary sources in the southwest and southeast Kalazha Formation, which thin out from south to north and vanish in the northern slope. Fan deltas occur in the southwest, and braided river deltas occur in the southeast. Kalazha reservoir rocks and sedimentary facies were predicted using joint 2D and 3D seismic impedance inversion. According to the overall analysis, the Kalazha Formation in the foreland slope is favorable for hydrocarbon accumulation, considering structural highs as the destination of long-term hydrocarbon migration and the updip wedge-out zone in the north with potential lithologic traps. The accumulation model was established with source rocks, reservoir rocks, caprocks, and migration systems for the lithologic hydrocarbon reservoirs in the Kalazha Formation in the SMJB. As per the model and regional stratigraphic and structural features, Kalazha lithologic hydrocarbon reservoirs mainly formed in the annular updip wedge-out zone in the foreland slope. Our deliverables may provide useful information for mass lithologic hydrocarbon accumulation in the foreland slope and deep to ultra-deep hydrocarbon exploration in the SMJB.
Highlights
Lithologic reservoirs, especially large and extremely large lithologic oil and gas fields, are important to hydrocarbon exploration and reserves and production increases, the proved reserves of which account for 80% of the total reserves (Yuan et al, 2003; Jia et al, 2007; Tao et al, 2017)
We focused on the sedimentation, reservoirs, and hydrocarbon accumulation in the Jurassic Kalazha Formation in the south marginal Junggar Basin (SMJB); a model of lithologic hydrocarbon accumulation was established in the slope zone of the foreland basin and predicted promising areas rich in lithologic reservoirs
Kalazha Formation were revealed in the SMJB based on individual-well analysis, cross-well stratigraphic correlation, well-tie calibration, and seismic reflections
Summary
Lithologic reservoirs, especially large and extremely large lithologic oil and gas fields (provinces), are important to hydrocarbon exploration and reserves and production increases, the proved reserves of which account for 80% of the total reserves (Yuan et al, 2003; Jia et al, 2007; Tao et al, 2017). As shown on the sedimentary system map, the Kalazha Formation in the southwest piedmont area is mainly composed of conglomerates (Figure 8) with large impedance, FIGURE 9 | A model showing hydrocarbon accumulation in Jurassic Kalazha lithologic reservoirs, the SMJB. Owing to the effect of buoyancy force, oil and gas will flow toward the shallow zones in the north along laterally connected sands in the Kalazha Formation and accumulate in those lithologic traps with top mudstone overburden to form lithologic hydrocarbon reservoirs. According to the accumulation model and stratigraphic and structural features of the Kalazha Formation, the promising prospects were anticipated to be lithologic traps in the annular zone, wedging out in the updip direction of the north slope, which has been the destination of hydrocarbon migration in a long period and is covered with thick mudstones in the updip direction. We should make full use of 2D and 3D seismic data to perform lithologic trap identification and prediction and offer support to gas exploration
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