Abstract:

       Reservoir space types, forming factors, and distribution of the Carbonferons volcanic rocks in Dixi area are investigated
by core inspection, thin section analyses, imaging logging, and seismic data interpretations. The results show that rock types of carboniferous volcanic reservoir in Dixi area include mainly basalt, syenite porphyry, volcanic breccia, and ignimbrite. Reservoir space can be divided into four types, namely primary pores, secondary pores, primary fractures, and secondary fractures. The primary pores are mainly gas pores and intergranular pores. Primary fractures include shrinkage induced joints and explosion related cracks. Intragranular dissolved pores and groundmass dissolution pores predominatec the secondary pores, and secondary fractures are prevailing tectonic fractures. The controlling factors of the reservoir space are volcanic lithology and facies, weathering and leaching, tectonism and dissolution. The types and distribution of primary reservoir space are controlled by lithology and facies, while secondary pore space and fracture are governed by the later three factors. From the northwest to the southeast, the controlling factors changed from the volcanic lithology and facies to the weathering and leaching, tectonism and dissolution. According to these, the gas pores and intergranular pores in Dixi 17 and 14 well area, are controlled by lithology and facies, resulting in a northeast-trending long strip. The secondary dissolved pores in ignimbrite and volcanic breccia from Dixi 10 well area occur along the fractures. The development of intragranular and groundmass dissolution pores are controlled by both the subvolcanic intrusives and fractures in Dixi 18 well area.

Key words: volcanic reservoir space, controlling factor, distribution, Carboniferous, Dixi area