Understanding the sedimentary sequence and architecture is important for planning the development strategy. We illustrate a case study of analyzing the sequence and architecture of a sandy conglomerate reservoir by integrating geology, petrophysics, seismic, and development data. The analysis indicates that the depostional environment of the target lower part of the Ganchaigou Formation is an alluvial fan. We defined eight lithofacies according to the core analysis and five sedimentary microfacies by integrating the core and petrophysical data. We next propose four sedimentary architectural models by integrating the lithofacies result, microfacies analysis, and high frequency sequence models. The four architecture models include the extensively connecting body sandwiched with intermittent channels, the composite channel formed by the overlapping and separation of stable channels, the lateral alternated braided channel and sheet flow sediment, and the runoff channel inlaid in flood plain mudstone. We finally build an architecture model for the alluvial fan. The model of the alluvial fan overall shows an upward-fining grain-size features and this feature indicates that the alluvial fan belongs to a retrograding sequence. The built model consists of six alluvial fan bodies that migrates from north.
Located in east part of Yingxiongling structural belt in the Qaidam Basin, the Yingdong oilfield has a extremely complicated ground condition. Due to no significant discovery, this oilfield was considered to have no favorable geologic conditions for formation of oil or gas reservoir. In the past few years, with continuous improvement in the mountain 3D seismic surveys and logging data interpretation, some breakthroughs were obtained in 2010, and the Yingdong oilfield, the largest-scale reserves of a single reservoir with highest organic matter abundance, most favorable physical property and optimal development efficiencies in the Qaidam Basin, had been discovered, the production capacity was up to 0.55 × 106 t. Through detailed analyses of the Yingdong oilfield, some studies, such as hydrocarbon accumulation conditions and technical challenges, are carried out, and following conclusions can be achieved. The Yingxiongling area is located in Mangya hydrocarbon-generation sag in the west part of the Qaidam Basin, its oil sources are rich; the Neogene Xiayoushashan Formation and Shangyoushashan Formation are dominated by wide and gentle delta front—shore-shallow lacustrine sediments with interbeds of sandstone and mudstone, the sandbodies are widely distributed with favorable physical condition, and the mudstone is the key caprock, combined with high-quality Paleogene hydrocarbon source rocks, a complete source-reservoir-cap assemblage can be formed. Large-scale detachment faults of the Yingdong area connect high-quality Paleogene hydrocarbon source rocks with middle-shallow buried structural traps, thus, reservoirs formed in the early stage are modified, and at the same time, hydrocarbons formed in the later stage continue to migrate and accumulate; in this way, the deep and shallow faults form a relay-style hydrocarbon transport system, and hydrocarbons are accumulated in the shallow structural traps in the later stage; in this area, the middle-shallow faults have good lateral plugging performance which is favorable for preservation of oil and gas. For complex landforms and reservoir features in the Yingdong area, the integral 3D seismic acquisition, processing and interpretation technology is developed for complex mountain areas to provide a reliable foundation for hydrocarbon exploration. For some problems in the Yingdong oilfield like long oil/gas-bearing intervals, great difficulty in identification of fluids, the development mode of multiple oil/gas/water systems in the long intervals is established, and the geologic modeling technology with constraint of multiple conditions on complex fault blocks is also developed. Thus, hydrocarbon accumulation mechanism in the Yingdong oilfield is clear, and some complex key technology of engineering are well solved, providing necessary geologic theories and technical supports for high-efficiency development and rapid production construction in the Yingdong oilfield.
Based on the data of field outcrops, drilling cores, casting thin sections, well logging interpretation, oil/gas shows during drilling, and oil/gas testing results, and combined with modern salt-lake sediments in the Qinghai Lake, the Neogene saline lake beach-bars in southwestern Qaidam Basin are studied from the perspective of sedimentary characteristics, development patterns, sand control factors, and hydrocarbon accumulation characteristics. Beach-bar sand bodies are widely developed in the Neogene saline lake basin, and they are lithologically fine sandstone and siltstone, with wavy bedding, low-angle cross bedding, and lenticular-vein bedding. In view of spatial-temporal distribution, the beach-bar sand bodies are stacked in multiple stages vertically, migratory laterally, and extensive and continuous in NW−SE trending pattern in the plane. The stacking area of the Neogene beach-bar sandstone is predicted to be 3 000 km2. The water salinity affects the sedimentation rate and offshore distance of beach-bar sandstone, and the debris input from the source area affects the scale and enrichment of beach-bar sandstone. The ancient landform controls the morphology and stacking style of beach-bar sandstone, and the northwest monsoon driving effect controls the long-axis extension direction of beach-bar sandstone. The beach-bars have a reservoir-forming feature of "one reservoir in one sand body", with thick beach-bar sand bodies controlling the effective reservoir distribution and oil-source faults controlling the oil/gas migration and accumulation direction. Three favorable exploration target zones in Zhahaquan, Yingdong−eastern Wunan and Huatugou areas are proposed based on the analysis of reservoir-forming elements.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)