Research On Evaluation Methods Of Cement Samples Damaged By Exploding Wave

As development of petroleum industry, low permeability reservoir plays more and more important role in petroleum exploration and exploitation. A technique used in low permeability oil fields named"exploding in oil layers"was brought forward after having absorbed lessons of High Energy Gas Fracturing and Hydraulic Fracturing. This technology can improve reservoir permeability, thereby increasing recovery ratio and economic benefit of fields.This thesis is about laboratory experiment evaluation research on increase production technology for low permeability reservoir. The rock damage and fracture by shock wave in"exploding in oil layers"can be simulated by the experiment of exploding on the surface of the cement sample in deep water by predecessor. Based on the exploding experiment, this thesis adopts experimental and calculational methods to evaluate the damage effect of cement sample, and get the enhancement of permeability of cement sample.Based on damage mechanism and appearance, damage zones were plotted out. After supersonic wave test, porosity test and permeability survey experiment, damage effect of cement sample by exploding wave was evaluated through theoretical analysis and sample observation. The relative damage factor was defined by the ratio of cement sample elastic modulus before and after exploding, and the damage factor can be explained by acoustic wave. Through dimensional analysis, the conclusion that the exploding wave pressure played the most important role in cement sample damage was gotten, and the relationship between zero dimension exploding wave and zero dimension cement sample damage was gotten by associating with experiment. Selecting the relationship model between fracture porosity and acoustic wave velocity and banding with the porosity experiment, the relationship of fracture porosity and cement sample damage was certained. Through analyzing the damage mechanism of cement sample, assuming a fracture seepage that the orientations of fractures damaged by exploding wave are different but the widths were the same to get the relationship between fracture porosity and fracture permeability. In summary, the relationship of exploding wave pressure and fracture permeability was gotten, and the optimum loading which can mostly increase sample permeability is established.The length of some macro fractures of cement sample is longer, so it's hard to evaluate the whole cement sample by experiment after coring. Based on fractures damage mechanism and sample appearance, firstly assume the width, obliquity, azimuth and density of fracture obey their own absolute random distribution, which form a disperse fractures system, the permeability distribution can be obtained by permeability experiment, then the permeability of sample can be calculated. Based on the relationship between tension damage scale and charge scale, the fracture scale and permeability of sample system under different exploding loading can be calculated. At the same time, the deformation effect of fractures at some confining pressure was analyzed, the deformation results in permeability decrease, so the relationship between fracture and confining pressure can be obtained. Through calculating, the permeability of fracture system after exploding is obviously higher than original sample at certain confining pressure.