The Variation Of Formation Compression In The Course Of Subsidence And Uplift Denudation Of Basin And Forecasting Method

The dissertation researches evolvement and character of formation compression by model test and geology analyzing, based on analyzing transformation of porosity, permeability, compressibility and density of sandstone and mudstone and fracture during subsidence and uplift. The conclusions are following:1. The basic factors influencing formation compression are thickness and density of overburden (including fluid)and behavior to enclose fluid of the formation.2. The variation of formation compression during subsidenceDuring the subsidence there are hydrostatic pressure and abnormal pressure zones in vertical. The appearance of abnormal pressure is related to lithology, lithology association, porosity permeability and compressibility of rock.It is vital difference for the changes of porosity and permeability between sandstone and mudstone. The permeability of sandstone is much bigger than that of mudstone under the same condition. Along with the increase of deepness, to porosity and permeability, mudstone reduce much more than sandstone.Due to the above reason the association of sandstone and mudstone is important to the form of abnormal pressure zones. It is possible to form abnormal pressure in the fleet stratum because the fluid of sandstone can not be expelled effectively in the sandstone lens closed down by mudstone. As a result of the fluid in the mudstone not effectively expelled because of the reducing of permeability in the side of mudstone, abnormal pressure is formed in the alternating layers of sandstone and mudstone. Hydrostatic pressure is kept because the fluid of sandstone can be expelled easily. Abnormal pressure is also formed in the thickness mudstone because the permeability of mudstone meet with sandstone decrease sharply which make the inner fluid not be expelled effectively.Forming of hydrocarbon and fission of oil which increase the bulk of fluid will lead the increase of formation compression in the stratum enclosed well.Fracture will form when the formation compression increase to the value of making rock break. It will release pressure.3. The variation of formation compression during uplift and degradationThe uplift and denudation of basin have a greatly influence to the formation compression formed previously. The fashion of influence is related to the uniformity extent of degradation of the earth's surface. Under the condition of uniformity degradation the formation compression will have a whole fall on account of the reduce of overburden, the expanding of fluid hi the pore and rocks and the decrease of density. Abnormal pressure is formed by uneven degradation causing a great elevation difference.4. The forecast method of formation compressionThe principle of forecast method is based on increasing of formation compressionalong with burial depth. The used parameters include velocity, density, porosity, and fluid content etc. In fact, the factor influence formation compression is very complex. It is related to lithology, lithology association porosity, permeability, compressibility of rock, enclosing and fracture etc. Therefore, it is important for the forecast of formation compression to consider fully the variation of each geology factor.