Characteristic Of Pore Space And Evaluation On Reservoir Of Acid Volcanic Rocks

Since most of the volcanic reservoirs discovered in the world are intermediate rocks and basic rocks, little attention has been paid to the acid rock reservoir. A typical acid rock reservoir was discovered from Yingcheng Formation in the north of Songliao basin. Complex applying core data, logging data and seismic data, this dissertation is devoted to study systematically on this special reservoir, such as characteristic of pore space, diagenesis, characteristic of parameters in developing, reservoir evaluation, and so on. The research results may have theoretical value in profound understanding the forming mechanics of acid rock reservoir, and also provide practical guiding in gas exploration and developmentReservoir space consists of pore and fissure in acid volcanic rocks. The principal pore types are primary pore and secondary solution pore, while most of the fissures are tectonic fissure and its strike is northwest-southeast and northeast-southwest. Diagenesis can be divided destructive type and constructive type. Pressure dissolution, welded action and filling are the most destructive action; while dissolution is the most important action in secondary pore formation. Volcanic clastic lava is dissolving easily, and rhyolite is difficult to dissolve. Volcanic clastic rocks are between them.Pore structure can be classified five types in acid volcanic rocks. Type I is combined with intergranular dissolving pore, gas pore and micropore, and has high porosity and permeability; Type II is composed of intergranular pore, intergranular dissolving pore, intragranular pore, intragranular dissolving pore and micropore, and has moderate porosity and permeability; Type III consists of intragranular dissolving pore and micropore, and has low porosity and permeability; Type IV has similar pore types to Type II, but its porosity and permeability is much low; Type V is made up of intergranular pore and micropore, and has very low porosity and permeability. breccia lava and gas pore rhyolite has the best pore structure, and most of them are Type I and Type II; welded breccia is the second, and its pore structure is mainly composed of Type I, Type II and Type III; welded tuff, crystal fragment tuff and volcanic breccia is the third, and its pore structure mainly consists of Type III, Type IV and Type V.The analyses for properties of whole-diameter core are indicated as follows: acid volcanic rock reservoir is extra-low permeable gas pool with heavy heterogeneity; the relation of rock porosity vs. net overburden pressure satisfies linear or pour function; the relation of rock compression coefficient vs. net overburden pressure meets pour function; at the beginning of net overburden pressure change, stress sensitivity of permeability is strong, but at the last period, its sensitivity is weak; the index of stress sensitivity gradually increases with net overburden pressure heightening; startup pressure gradient raises with the decreasing of atmosphere permeability and its relation with fluidity satisfies pour function, but it is independent of bound water saturation; volcanic rock reservoir is provided with weak velocity sensitivity.Development of acid rock reservoir may be controlled by lithology, facies, diagenesis and tectonic action. The formation and amount of primary pore in volcanic rocks is up to lithology and facies. Diagenesis has critical affection on preservation of primary pore and formation of secondary pore. Tectonic action may play an important role in the evening reconstruction of volcanic reservoir and fissure developing.Acid volcanic rocks can be divided five types: Type I has good porosity and permeability and high production, and gas can be produced naturally. This type is mainly distributed in breccia lava and gas pore rhyolite. Type II has medium porosity and permeability and high production, but needs compression fracture. These reservoirs are welded tuff, crystal fragment tuff, and gas pore rhyolite. Type III has low porosity and permeability and low production, the rocks are welded tuff, crystal fragment tuff, welded breccia and gas pore rhyolite. Type IV has much lower porosity and permeability and production. This type is non-industrial reservoir and mainly in welded tuff, crystal fragment tuff, welded breccia and low-gas pore rhyolite. Type V has extra-low porosity and permeability, and is non-reservoir. They are mainly volcanic breccia and dense rhyolite.