Analysis Of Rock Fracturing Characteristics And In-situ Stress

The fracability of rock is one of important evaluation parameters in the exploitation of oil and gas fields,which is applied to evaluate reservoir fracturing feasibility,to forecast fracturing effect and to select fractured wells.Many researchers put forward different evaluation methods for different research purposes,but they have not reached a common agreement yet.In this paper,the fracturing properties of rock and geo-stress of oil fields are studied in ways of the mechanical parameters testing,acoustic testing,analysis of logging data and field construction fracturing data.The main contents and conclusions include:(1)Firstly,static mechanical parameters of the cores were measured by rock mechanics test indoors;based on stress-strain curve,the characteristics of deformation,strength and energy during rock fracture damage were analyzed for an accurate assessment of rock fracturing characteristics;the plane elastic modulus,elongation index,plasticity index is taken as the index fracture characteristics for the first time in this paper.Combined with plastic strain energy analysis during compression fracture,rock brittleness index,the overall evaluation of the fracture characteristics of rock was made;fitting relationship among the indexes,it was found that they have good correlation;fracture properties of the rock can be evaluated in different ways.(2)Fracture characteristics of rocks can be evaluated from various aspects by use of static mechanics parameters.But the static mechanics parameter of rock is time-consuming and labor-consuming.A new method is proposed to evaluate the formation compressibility in this paper,which is based on the dynamic parameters of logging data.Obtaining vertical and horizontal wave velocity through the acoustic test of the cores,calculating dynamic rock mechanics parameters,and analyzing static and dynamic rock mechanics parameters,it was found that the two parameters had good simulation effect,and a formula reflecting the conversion relationship between the two parameters was established.,the relationship between the two parameters are quite different in different blocks and different lithology.Therefore,the static value can be gotten through the converting relationship between the two parameters even if indoor mechanical parameters aren't test.The method is worth using widely to evaluate the rock fracturing characteristics.(3)The study of the geo-stress and its measuring method.The basic principles and methods of hydraulic fracturing stress measurement are explained in detail,and the method of reading the closing pressure,burst pressure and reopening pressure on the fracturing curve is clearly put forward.Combined with the curve of on-site construction fracturing,the value of each closure pressure wells are measured in three ways.Calculating the maximum and minimum stress values of the exploration block,and analyzing the relationship between the two geo-stress values and the depth,the fitting formula is determined.