Firstly, the extrusion of magma causes brittle fracture of carbonate rocks, resulting in a large number of tensile cracks; Secondly, the high temperature of magma decomposes or gasifies calcium carbonate and organic matter, producing carbon dioxide and hydrocarbons, resulting in a large number of holes; Furthermore, the acidic components in magmatic fluid can significantly dissolve calcium carbonate, resulting in a large number of dissolved pores.
Through field and core observation, it is found that there are a large number of secondary pores such as cracks, dissolved pores and pores in carbonate rocks around intrusive rocks, which have excellent reservoir performance and oil and gas (including inorganic carbon dioxide gas) are often very developed. Such as the Ordovician reservoir of Boshen 6-5 well in Gu Xi fault zone of Zhanhua sag. There are three reservoir spaces in this section: the interpreted reservoir is 80.5m/ 13, of which the intrusive rock reservoir is 26m/5 (accounting for 32% of the total reservoir). The thickness of intrusive rocks in this well accounts for 23% of the total stratum, and the storage rate of intrusive rocks is 33% and the total storage rate is 23.2% (Figure 5-9). According to the reservoir distribution of Boshen 6-5 well, intrusive rocks and their vicinity are mainly developed in the reservoir, and the fundamental reason is the comprehensive action of intrusive rocks and their fluids on carbonate rocks, such as mechanical crushing, high-temperature gasification and chemical dissolution.
To sum up, magma and deep fluid make complex physical and chemical reactions of surrounding rock, which significantly improves the reservoir performance of surrounding rock. Due to the differences in composition, structure and structure of surrounding rocks, there are great differences between magma and deep fluids in their transformation, especially carbonate rocks, mudstone rich in organic matter and coal rocks.
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