Research On Test Methods For Rock Parameters In Tight Oil-Gas Reservoirs

Rock parameters test is one of the most necessary means to recognize the oil-gas characteristics of reservoirs. Recently, with the continuous tightening of global oil and gas resources, the oil and gas exploration of unconventional reservoirs such as low permeability, tight reservoirs, shale gas reservoirs etc. continued to make new breakthroughs. As a result, methods of testing the rock parameters are increasingly significant and complicated. In order to study on test methods for rock parameters in tight oil and gas reservoirs, many works have been done in this paper. Rock microscopic parameters including porosity, permeability, pore structure, movable water saturation are tested by several methods. The application has archived good results.After comparing the porosity obtained by water-measured porosity and gas-measured porosity, it is the first analyze the influence of the pressure on gas-measured porosity. The results show that test pressure plays important role in gas-measured porosity of tight reservoirs, so helium should be test medium. What’s more, gas-measured porosity with 200psi test pressure is more suitable to describe the rock characteristic parameters. And this gas-measured porosity can provide credible results to evaluate tight reservoir rock.Aim at characteristics of tight reservoir rock parameters, steady-state method was used to test rock gas log permeability. In the test, valid test pressure was set as 2MPa, and the best fitting Klinkenberg permeability outlet flow ranges from 1ml/min to 7.5ml/min to avoid turbulence or slipped. At the same time, the unsteady pulse decay method was adopted to test the rock permeability. Compared permeability resulted from two methods, it shows that unsteady pulse decay method is more convenient, and needs shorten time. So unsteady pulse decay method is more useful in testing permeability of tight reservoir rock.The rate controlled mercury injection and low-temperature nitrogen adsorption method are used to test rock parameters, such as micro-pore throat characteristics, pore volume, surface area and so on. Since controlled mercury injection to mercury pressure up to 900psi, corresponding to the throat radius of 0.12μm, and smaller pore throat cannot be measured, while the low-temperature nitrogen adsorption method just to make up for this shortcoming of the rate controlled mercury injection. It’s the first time to combine these two approaches to study on pore throat characteristics of the tight reservoir. It is concluded that the reservoir permeability is mainly determined by the distribution and size of the core throat, it means that throat is fluid seepage paths and reservoir fluid storage space. Mainstream throat radius should be used as one of the parameters of evaluation of tight reservoirs.Through the research on the movable water saturation of rock by a combination of nuclear magnetic resonance and the centrifugal force, it’s the first time to propose that the best centrifugal force (corresponding to the throat radius of 0.05μm) is 417psi, and then calibrate cut-off value of T2 of the rock. Since movable water saturation obtained by this method is independent from rock porosity and permeability, so this result can be used as one of the parameters of rock reservoirs.