Rock Physical Experiment And Fracturing Potential Characterization Of Shale Gas Reservoir

Today, declining production from depleting conventional oil and gas resources in the world, combined with increasing difficulty of exploration and development has driven demand for unconventional oil and gas resources. Shale gas is one of the most important unconventional resources. Petrophysical experiments are the foundation to understand shale reservoirs, and the the new well logging method applied to shale gas needs to be combined with petrophysical experiments to establish the high accuracy well logging interpretation model and to improve the accuracy of logging evaluation.Plunger cores with the diameter of 2.54cm (lin) or 3.81cm (1.5in) are required when performing laboratory measurements for petrophysical parameters that are closely related to the well logging such as porosity, permeability, resistivity, sonic velocity, fracture pressure, nuclear magnetic resonance, and etc. Shale rocks have the brittle and fragile characteristics, thus processing plunger cores to meet the experiment requirements is the bottleneck problem of the petrophysical experiment for shale gas reservoirs.Starting with the processing technology of the shale rock plunger core, this paper has solved the difficult processing problem of shale plunger core firstly. Then, taking the 2.54cm (lin) pluunger core as the research carrier, the research of measurement method of porosity and ultra-low permeability for shale rocks, the research of the petrophysical properties incluging acoustics, electricity, nuclear magnetic resonance, and etc., and the research on fracability characterization method are performed.Through research works described above, the understanding and conclusions have been gotten as follow:1. processing The diamond wire cutting and processing technology is introduced into area for the rock core of shale gas reservoirs which has resolved the processing problem of shale rock plunger cores, providing the guarantee for the petrophysical experiment research of shale gas reservoirs, avoiding the hydration and disintegrated problem as shale rocks meeting water when drilling and getting cores by using the traditional drill tube with water lubricating and cooling or by using the drill barrel with the liquid nitrogen cooling for uncemented loose rock samples. The developed system has been successfully used to process shale rock plunger cores that including the wire cutting, the digital program, and the cutting cleaning, which overcomes the brittle, fragile, hydration and disintegrated characteristics of shale rocks.2. The reason by using three methods of shale rock cores porosity measurement getting different shale porosity results is analyzed, which includes the helium method, the liquid method and the nuclear magnetic resonance method (NMR). The NMR porosity being bigger than usual is due to the dry shale rock core having nuclear magnetic signals and the source of the signal coming from clay minerals that montmorillonite containing a large amount of interlayer water. Helium porosity being smaller than usual is due to shale rock has a strong adsorption capacity and developing a large number of nano scale pores, which leading blocking by adsorption of oxygen and nitrogen molecules in the air, causing the micro pore of the shale rock is not fully filled with the measurement gas. The saturated liquid method can fully saturated core, which reflects the pore space of core. Therefore, for the shale rock core porosity measurement, the salt water porosity and the corrected NMR porosity shold been adopted.3. The permeability measurement technique of pulse attenuation method for shale rock cores is studied, and the factors that affect the length of permeability measurement, pore pressure and confining pressure are experiment researched. If the core is longer, that causes the measurement gas not fully to saturate core pores. The length of the core should be shortened to meet the requirements of the measurement process principle. Experimental results show that the length of the rock core should be controlled within 1cm. Pore pressure has little effect on the measurement value of the permeability, and has obvious influence on the attenuation rate. Net effective pressure has great influence on the measurement value of permeability. Therefore, it is proposed that simulates the formation of effective pressure to measure the permeability; the pulse pressure difference should be 10psi as measuring permeability.4. A method for fracability characterization of shale rock cores is proposed. The fracture pressure test technology of core constant velocity strain method was established. The CT scanning technique is used to reconstruct core. The fracture information after core fracturing test is quantitative analysed; characterize the fracture complexity by using the average value of the fracture after porosity and the degree of dispersion of the fracture angle being normalized. The definition of the core fracturing index is the ratio of fracture complexity and strength, in which the strength gotten by the core three axis compressive strength with eliminating size effect correction. This characterization method is a feasible evaluation model for shale fracturing that provides a laboratory evaluation method for shale gas reservoirs fracability.