Factured Mudstone Reservoir Forming Condition And Its Geophysical Characteristics In Qijia-Gulong Area

With the development of world oil industry, structural traps dominated era has ended in petroleum exploration. The exploration of unconventional oil is paid more and more attention, including fractured oil and gas reservoir. According to statistics, fractured reservoir is trapped more than10%of the oil reserves. In1980’s, mudstone fractured reservoirs was also found in Qingshankou Formation (K2qn) at Gulong area in the northern Songliao basin; up to now,6wells obtain industrial oil flow; by sketchy estimating, about180-440million tons oil conserves in mudstone-fractured reservoir in favorable areas, showing good exploration prospects.In this study, using theories from sedimentology, reservoir geology, seismic and well logging geology, comprehensive applied of geological, seismic, logging and test data, the researchers compared and analyzed the domestic and foreign fractured shale reservoirs. They studied mudstone fractured reservoir petrologic characteristics, fracture characteristics and cause of formation, mudstone-fractured reservoir geophysical response characteristics. At last, reservoir comprehensive analysis and prediction of favorable areas in Gulong were carried out.Main results and ideas of the research include:1. Proved that mudstone-fractured reservoirs of K2qn in Gulong have good resource base and prospect, because of high detained hydrocarbon content in source rock;2. For the first time, the systematic evaluation of the mudstone reservoir was done, including Lithology-mineral composition, microscopic pore structure and facies distribution characteristics, pointed out that reservoir rocks are mudstone, siltstone/Ostracoda limestone in thin layer, that reservoir space mainly includes vertical fracture, interlayer-micro fracture, residual hole, and described stone-facies distribution of K2qn in Gulong, pointed out the favorable facies distribution area;3. According to the genesis, mudstone fracture is divided into three categories, which includes structural, sedimentary-diagenesis and overpressure origin fracture, and hydrocarbon-generated overpressure on influenced the fracture formation in hydrocarbon accumulation period, meanwhile controlled oil and gas enrichment, because it made early fracture cracks open and filling oil gas;4. Having taken Bayanchagan blocks in Gulong as the experimental area, discussed geophysical recognition and prediction method of mudstone-fractured reservoirs, gas detection in well data could identify mudstone fracture more favorable, coherence and curvature of seismic attribute could predict fractured reservoir in some degree;5. Established mudstone fracture reservoir accumulation model of K2qn in Gulong, considered that the main control factors of reservoir forming is good hydrocarbon source rock, the favorable facies zone, favorable tectonic position and overpressure zone, then divided the favorable exploration area for mudstone-fractured reservoirs of K2qn in Gulong, and evaluated the exploration potential for the best blocks.