The Reservoir Evaluation And Porous Flow Mechanism For Typical Tight Oilfields

This research focused on four typical tight oilfields (Changqing, Sichuan, Dagang and Daqing), using low-temperature nitrogen adsorption, mercury injection with high pressure (MIHP), mercury injection with constant rate (MICR), NMR, centrifuge and physical simulation to comparative study the microscopic pore structure, pore types, characteristics of movable fluid, development limits and comprehensive classification method. On the basis of analyzing the impacts of micro-and nanoscale forces and EDL on flowing, what the state of being is analyzed for the fluid in the micro-nano channels and the viscosity correction method is proposed. And the new electrokinetic coupling model for flow in micro-nano channels is established. As for tight oil development, the experimental setup for measuring the resistance of solution gas drive is designed. And the mathematical model of resistance is proposed too. Meanwhile, the new model of solution gas drive is established. The main research results and findings are as follows:(1) According to deeply analysis the data of low-temperature nitrogen adsorption, MIHP, NMR and centrifuge, the measuring method for full-scale graph of tight reservoir cores’pore radius distribution through interpolating two times, connect one time and checking one time. Its application shows that the nanoscale and sub-micro pores almost take the whole space of tight reservoir cores. If the nanoscale pores take more than 60%, the reservoir would be very difficult to develop. The sub-micro pores contribute over 50% to the core’s permeability in Daqing and Changqing oilfields. But the permeability just relies on few micro pores and bedding fractures in Dagang oilfield.(2) The movable fluid research shows that the ratio of fluid controlled in nanoscale pores in tight carbonate is larger than that in tight sandstone. It demonstrates that the pores in tight carbonate are much smaller than those in tight sandstone. With the increase of permeability, the movable fluid in sub-micro and micro pores increase gradually. And ratio of movable fluid in tight sandstone is bigger than that in tight carbonate.(3) On the basis of full-scale graph of pore radius, the computing method of internal surface area for different scale spaces is established through the calculus thought. Meanwhile, synthesizing the full-scale graph and centrifuge-NMR data, the irreducible water volume can be calculated. Then the thickness of irreducible water also can be calculated. According to plotting the thickness of irreducible water against permeability, finding that development threshold of pore-throat is 22nm, and permeability is 0.08mD in Daqing oilfield, and that is 18nm and 0.03mD respectively in Changqing oil field.(4) According to adsorption/desorption isotherms, the matrix pore shape can be gotten. Through power exponent method, it shows that the type of Dagang tight reservoir is double-porosity system and the width of micro fracture is much bigger than the radius of pores. And that of Daqing is also double-porosity system, but the width of micro fracture is close to the radius of pores. Synthesizing the above factors, this paper has gotten the pore models of different tight oilfields and different lithology.(5) On the basis of low permeability reservoir comprehensive classification, the "Seven-elements Comprehensive classification coefficient" for tight reservoir is constructed composed of average throat radius, movable fluid percent, threshold pressure gradient, clay mineral percent, oil viscosity, formation pressure coefficient and brittleness. This evaluation method establishes the foundation for the comprehensive classification of tight reservoir.(6) What the state of being is analyzed for the fluid in the micro- and nanoscale channel. The correction method of viscosity is proposed. According to research, the primary forces are surface forces. The liquid exists as EDL fluid and bulk fluid. Correcting the viscosity of the EDL fluid, and from the theory of Hagen-Poiseuille flow and electroosmotic flow, the new electrokinetic coupling model is gotten. The theoretical research results are roughly identical to corresponding experiments by researchers in the same field. Meanwhile, the experiments are explained using the electrokinetic coupling theory.(7) According to the thought of Henri Darcy experiment (presenting the different micro- and nanoscale effect as permeability, K, then the complex problem become much more simple), the resistance measuring system for solution gas drive has been designed. The experiment shows that the resistance is changing as exponential form. On this basis, the new model of solution gas drive has been gotten. Coupling with the nonlinear elastic drive, it finds that drainage radius of solution gas drive is very small and decreases sharply around the bubble point. Closer to the well, the pressure changes more sharply. And the production of solution gas drive is very low.