Research And Application Of Formation Pressure Prediction For Infill Adjustment Well Drilling

Due to the various downhole operations after the oilfield being put into production, such as acidizing, fracturing, water injection, and so on, all of the properties of formation porosity, permeability, pore throat diameter are changed, the distribution of formation pore pressure also changes from the relative stable state to the unstable dynamic. It is of theoretical and applicable meaningful value to study the method to predict the formation pressure during drilling infill adjustment well under this dynamic condition.In this dissertation, based on the geological characteristics of multi-heterogenous layer system, development model of multiple well patterns, various displacement style, and according to the correlated static and dynamic data of well logging, drilling, exploration and development data base, the formation may be drilled during the third time infill adjustment well drilling and its physical properties are predicted. Based on the theory of fluid mechanics in porous media and reservoir performance, the pressure distribution principle is studied for the complex pressure system formation the adjustment well to be drilled in under the condition of production and injection, the mathematic model for predicting the formation pressure under the condition of injection and production is established. The applied procedure for pressure profile adjustment is given, a dynamic formation pressure prediction method for adjustment well drilling is provided, and the applied software based on the formation pressure prediction model is developed. The work of this dissertation technically guide the formation pressure adjustment and control in the third time infill adjustiment well drilling in Lasaxing oil field.Firstly, the pore structures of the 986 cores from 28 wells in Lamadian oil field are analyzed by mercury determination, and the size and distribution of pores, the connection relation of pore and throat, the geometric of pore, the micro-heterogeneity, the composition and distribution of mineral in the pore are determined. It is appointed out that using DS phase control to construct model can develop the accuracy of formation perameter predicton. The DS phase control modeling principle-based formation permeability prediction model and sand rock thickness predition model are given. According to the gray system theory, the porosity prediction model is established using seismic, well logging, drilling data. The seismic and well logging data of 3 wells in Daqing oilfield are dealed by Biot method, and on the basis, the applied procedure to predict the effective thickness of sand rock layer is suggested, and the horizontal distribution of effective thickness of sand rock layer of Putaohua oil reservoir is given.Secondely, it is found through analysis on Daqing Lasaxing reservoir data that the horizontal and interlaminer contradiction are serious in the water-flooded multi-layer heterogeneous reservoir, and to increase water injection in the front phase will help to reduce this kind of contradiction. Through layers division, to develop independently by different well pattern can reduce the interlaminer contradiction or interference, keeping the balance of formation distribution, improving the development effect. On the basis, four well spacing principles are suggested, the reasonable well space should be controlled in 100 to 150m in the thin and poor oil layer and untabulated reservoir. The reasonable well density should be controlled in 60 wells/km~2 when drill the third time infill well in the Bei3 region. If five-spot water injection pattern being adopted, the third time infill well density should be 144 wells/9.4km~2 in the economical area of Bei3 region, and 65 wells/4.3km~2 in the risk area, 98 wells/6.5km~2 for the preparation area. After the third time infill well being put into production in the East part of Bei3 region, the natural declining rate of the old wells decreases from 12.89% to 11.54% and good effect is achieved.Thirdly, investigation shows that in the intial stage of high water content period, the extra high and high water cut layers with high pressure will interfere the high, middle and low water content layers with low pressure. In the late stage of high water content period, with the continuous increase of water cut, the form of interlaminar interference will change into the interference of high and extra high water content layer with high pressure on the middle and high water content layers with low pressure. The reasons of interlaminar interference are analyzed, and applied method to solve the problem is provided. It is regarded that the adjustment form of injection-production system of Daqing oilfield at the high water content stage should not only depend on the old oil well changing into injection, but taking old oil well changing into injection as the main means, combining various procedures such as adding perforation, adding well, mutual support of well pattern. Through overall consideration on the connection between conversion wells and various sets of well patterns, to increase the ratio of multi-directional connected thickness, so as to improve the water flooding control degree, and excavate the potential residual oil. It is appointed out that when the flow pressure in the production well keep constant, if the injecton to production ratio is bigger than 1, then the formation pressure at the production well will rise. With the increase of oil well number, the formation pressure will drop gradually. Otherwise, the formation pressure will rise. On the basis of analysis on high pressure regions of lighology, casing failure, triangle of fault injection well drain, regional water-plugging of oil production well and hiding type abnomal area, the causes of formation are provided. It is appointed out that if injection is bigger than the production, layer of high pressure will be caused, otherwise, low pressure layer will be formed, if the injection and production keeps banlance, the normal pressure layer will be achieved, then the high, low and normal pressure layers will appear alternately, so in the reservoir with water flooding development, the profile of multi-pressure layers at the vertical direction will be formed, which pose great difficulty to the adjustment well drilling.Fourthly, facing the fact of multi-pressure series formed after water injection development in Daqing oilfield, the mathematical models are constructed for stable production, unstable production and pressure distribution after well drilling. According to the the theory of fluid mechanics in porous media and superposition principle, the theoretic pressure distribution model for any point in the formation under the condition of multi-wells interference is established. The geological database for the reservoir in which the adjustment well to be drilled is constructed. The formation pressure prediction simulation software for the infill adjustment well drilling is developed, and a set of applied methods of formation pressure prediction for infill adjustment well drilling is formed. The reasonable drilling and shut-in range, reasonable drilling and shut-in time, pressure drop pattern for water injection well is provided. The drawing technique for longitudinal pressure profile of the reservoir the infill adjustment wells being drilled is provided, the longitudinal pressure profile and pressure isogram are made. It is showed that under the normal condition of production and injection and under the condition of drilling shut-in, the formation pressure profile chart can express the formation pressure distribution principle, which can realtimely guide the drilling process planning and borehole problem treating.At last, the foundation for adjusting the formation longitudinal pressure profile are suggested. The pressure coefficient and inter-layer pressure difference control range are given. According to the type of abnomal pressure region, different formation pressure profile adjustment technologies are given. The real drilling applied principles of drilling shut-in decompression, flow-off decompression and pressure keeping water injection are studied. The combination of these procedures makes the formation pressure profile adjustment method more reasonable. The often used adjustment well drilling shut-in scheme for the East part of the Naner region is optimized by using the theory of this dissertation. After the new shut-in scheme suggested in this dissertation being applied, the ratio of high cementation quality in this region increases 5%, up to 74.67%. Pressure maintaining water injection application tests are carried out by using the theoretic computation and optimized water injection parameters, the interlayer pressure difference reduces 0.92MPa in the middle region test well, and this value is 1.06MPa in the Naner region, obvious pressure reduction effect is achieved. It is shown from the tests that the investigation results achieved in this dissertation can be popularized and applied in the pressure prediction, adjustment and control project carried out in the infill adjustment well drilling formation.