| West Sichuan Depression, located in western Sichuan Basin, is deep depression part of the basin since the Late Triassic. West Sichuan Depression have developed many sets of hydrocarbon source beds, a number of hydrocarbon source area, multi-phase oil and gas generation and accumulation, also have accompanied several tectonic adjustments and destruction episodes, so there were several sets of source-reservoir-cap system in vertical.Since 11th five-year plan, Exploration and Production Research Institute of Southwest Branch Company has achieved remarkable success in deep formation gas exploration in Middle West Sichuan Depression, but as exploration degree and difficulty of shallow and middle formation is getting higher and higher, stable yield situation of shallow gas reservoirs, such as Xinchang, Luodai gas fields is becoming more pessimistical.Shaximiao gas reservoir itself has a low porosity and permeability, low abundance, as well as traps in the study area characterized by the formation of a complex history. Based on sequence stratigraphy studies and combined use of various other methods, the paper systematically studied Shaximiao sedimentary facies characteristics, and evaluated different block reservoir characteristics of Shaximiao formation, then comprehensively analyzed Shaximiao formation accumulation controlling factors.The main access to knowledge and innovative results are as follows:(1) On the basis of previous research, the outcrop, drilling, seismic sequence boundary identification at different levels and sequence structure and stacking pattern studies, combined with sedimentary cycle characteristics of the study area, the Shaximiao formation is divided into 3 long and 8 intermediate-term cycles, and isochronous comparison of Shaximiao formation over whole study region is achieved(2) Depositional paleotopography was studies by using of the color weight value for shale in the West Sichuan depression for the first time. The shale color weight value of central zhixinchang and hexingchang region is higher than that of it both sides in middle period of upper Shaximiao deposition, this indicates the area remain at a relatively oxidizing environment, water depth was relatively shallow, that is, the structural belt has begun to take place, and this also further proved Longmen Mountains to napping toward the basin and Stress Transfer during period of Shaximiao deposition.(3) By single-factor analysis methods, such an the thickness of sandstone, ratio of sand to mud, shale color weight value, heavy and light mineral characteristics, outcrops and logging paleocurrent, as well as by comprehensive analysis on the single-well phase, profile phase, logging phase and seismic facies, the material source changes, sedimentary evolution and distribution of sedimentary facies of Shaximiao formation was systematically studied , the results are as follows:1) There are two primary provenances of Shaximiao formation: one is the northern section of the Longmen Mts metamorphic rocks, and the other is central section of Longmen Mts acid igneous rocks, the two main paleoflow was to the NEE and SE respectively.2)The northern section of Longmen Mts provenance-depositional system was poor feldspar, high-quartz light mineral characteristics during period of Shaximiao , by contrary, the central section of Longmen Mts provenance-depositional system is charactered with feldspar-rich, low-quartz light mineral.3) Two different facies Association were identified in shaximiao formation, the lower Shaximiao formation mainly Consists of prodelta and lacustrine depositional systems, the upper shaximiao formation are formed by the delta plain,prodelta and lacustrine depositional systems. This show that the Longmen Mts thrusts push over towards basin during Shaximiao period gradually.(4) Based on the macro-analysis of provenance, deposition rate, paleotopography and the micro-analysis of reservoir rock characteristics, diagenesis, porosity evolution, the effects of the main diagenetic type,intensity and sedimentary on reservoir quality are studied, and also the geological prediction method about relatively high porosity and permeability is also established initially. The Predicted results show that the underwater distributary channel and mouth bar sands body which are relatively low paleotopography, moderate deposition rate and feldspar-rich are relatively better. (5) Shaximiao reservoir parameters of logging calculation model is improved based on different area and strata in western Sichuan basin, the logging response characteristics of reservoir fluid was further summarized, and reservoir fluid checking Method and evaluation criteria are improved. The logging response characteristics of Shaximiao gas reservoir are low natural gamma, low-neutron, low-density, high-sound waves and high resistivity.(6) By basin modeling, shaximaio formation palaeostructure is recovered at the end of the Late Cretaceous, Early Cretaceous, and Penglaizhen period respectively. From period of the Shaximiao and Suining deposition to the end of Early Cretaceous, the Shaximiao structure shapes was higher in the South than in the north; Late Cretaceous, the Peng xian- Chongzhou region of middle West Sichuan Depression was a depression, and xiaoquan - xinchang - hexiangchang - Feng Gu structural uplift occurred. Luodai-zhongjiang- Dayi regions at the end of Late Cretaceous,Early Cretaceous and Penglaizhen period was the inherited structure high.(7) Accumulation model—episodic accumulation model of the shallow and mid formation with weak deformation is summed up, the model clearly points out that the episodic accumulation model is charactered with near-source accumulation, namely, the Lower Jurassic with weak deformation is the better exploration prospects; Controlling factors of the source -fault of hydrocarbon accumulation mode is improved , namely, size of contact surface between reservoir and source fault is the basic factor that affects lateral migration and accumulation of oil and gas, so exploration should focus on the seismic anomaly and fault configuration description.
|
PDF Full Text Request