Compact sandstone micro-pore structure characterization method

Abstract

The invention discloses a compact sandstone micro-pore structure characterization method. The method comprises the steps of firstly, dividing a casting body sheet into different pore units, extractinga picture of pores in each unit, counting the area and perimeter of each pore, and calculating shape factors of the corresponding pores; calculating corresponding pore radiuses based on pore radius calculation formulas of different shapes; then, combining the pore distribution in the casting body sheet and the characteristics of a constant-speed mercury injection curve, and simultaneously combining the throat distribution obtained by high-pressure mercury injection with the corrected constant-speed mercury injection throat distribution to obtain the complete throat distribution of the rock core; and finally, based on the shape factor distribution obtained by the casting body sheet, respectively proposing pore radius of the rock core and a distribution characterization method thereof whenpore shape distribution is stable and pore shape distribution difference is large. According to the method, the defects of various existing microcosmic pore structure characterization methods are overcome, and the obtained complete pore and throat sizes of the compact rock and the data of distribution thereof are more accurate.

Description

technical field [0001] The invention relates to the technical field of unconventional oil and gas exploration, in particular to a method for characterizing the microscopic pore structure of tight sandstone. Background technique [0002] Tight oil is another hot spot in the field of unconventional oil and gas exploration and development in the world after shale, and has become one of the important future energy sources in my country. In the process of exploration and development of tight reservoirs, there are obvious differences from medium and high permeability reservoirs in that tight reservoir rocks have fine particles, low porosity and permeability, strong compaction during the diagenesis process, and complex microscopic pore structures , the pore throats are mostly micro-nano scale. Accurately characterizing the microscopic pore-throat structure of tight reservoir rocks, and clarifying the size and distribution of pores and throats in tight reservoirs are of great pract...

AI Technical Summary

Problems solved by technology

However, in the amount of mercury injection, if the volume of this part of the cavity is added to the mercury injection of the total pore-throat system, the value of the mercury injection saturation will be too large. This phenomenon is called the hemp skin effect.

Affected by the hemp skin effect, the mercury saturation is too high, the capillary curve drawn is distorted, and the pore size and distribution represented have large errors; in addition, the maximum mercury injection pressure for constant-speed mercury injection is 1000Psi (6.9MPa), the lower limit of the reflected pore-throat radius is 0.12μm, and the pore-throat below 0.12μm cannot be characterized

[0007] (3) Although the pore-throat information given by high-pressure mercury intrusion mainly reflects the distribution of throats, there are still some small-radius pore distributions superimposed on it, so the obtained throat information is incomplete

[0008] (4) In addition, in the conventional constant-speed mercury injection and high-pressure mercury injection data processing, the pores are equivalent to spheres and the corresponding equivalent sphere radius is calculated using the Washburn formula to characterize the size and distribution of rock pores, but this is not It is not suitable for tight reservoir sandstones that have experienced strong compaction and cementation and irregular pore shapes, which will cause the calculated value to be too large

[0009] (5) NMR technology can obtain complete pore throat information, but cannot directly obtain pore throat radius distribution

At the same time, the NMR T 2 When the relaxation time is transformed into the distribution of pore throats, the core pore shape is generally regarded as a fixed value, and the characterization method of the pore radius when the core pore shape is greatly different is not considered.

Images