Characteristics and controlling factors of fractures in igneous rock reservoirs

Based on the updated exploration and research achievements, this paper studies the types and controlling factors of the fractures in Carboniferous igneous rocks of Northern Xinjiang, and their influences on the high-quality reservoir and high production of oil and gas. Fractures with different occurrences (oblique fracture, net fracture, horizontal fracture and vertical fracture) and geneses (autoclasic fracture, contraction fracture, dissolved fracture, joint fracture and structural fracture) were developed in igneous rocks. The ability of fluid flow and seepage radius were different in various fractures. The development degree of fractures was controlled by lithology, tectonic movement, early and late diagenesis. It was controlled mainly by lithology in the areas of weak tectonic movement; it varied in different lithologic igneous rocks with the same tectonic background. The main controlling factors of forming fractures in igneous rocks were tectonic movement, late and early diagenesis, especially tectonic movement and hypergenesis during the stage of late diagenesis. Various lithologic igneous rocks undergoing intense tectonic movement and long-time weathering developed fractures and favorable volcanic reservoirs that were concentrated in the area no more than 3 km away from the main fault zone. The closer to the fault the well is located, the easier it gains high and stable production of oil and gas.