Adjustment Wells In Dagang Oilfield Formation Pore Pressure Prediction Research

After experienced the stage of relying on the exploitation of natural energy and water injection,onshore oilfield is entering into the middle and later periods of oilfield development. In order to stabilize oil and gas production and to enhance oil recovery, it must through drilling adjustment well and constantly improve and develop well pattern.Due to years of injection-production, the developed fields will inevitably cause the reservoir pressure depletion, it also will break the original pressure balance system, became the cause of facing pressure deficit zone and pressure-out zone during drilling adjustment wells. Leakage,resistance,stuck,collapse,spray and other complex accident will happen, even result in borehole obsolescence. Therefore, an accurate prediction of the pore pressure on horizontal and vertical distribution is essential to protect the safety of quick drilling.Block G128 of Dagang shenjiapu field is taken as the research object In this paper. After 15 years of water-flooding, the casing-damaged is serious that result in well pattern paralysis,there are conflictions in development and it’s difficult to get stable block production. For the sake of improving the development level of block, the essay takes perfecting and exploiting well pattern by drilling adjustment wells as the background. Carring out integrated multidisciplinary depth prediction of developed oil-gas-field abnormal formation pressure, calculating, analysing and simulating the original formation pressure and current formation pressure after failure through three parts----drilling, geological modeling and numerical reservoir simulation, summarizing the pattern of the formation pressure horizontal and vertical distribution on block G128. The main results are as follows:(1) Choose the calculation model of acoustic time difference method through formation lithology and initial drilling data of block G128. First step is to calculate Eaton index of block on the base of the original measured value of formation pressure. Then calculate the original formation pore pressure of block in nine representative wells, and to draw the horizontal and vertical distribution of it. Without considering the impact of pressure transmission on cap formation, using Morita’s theory to calculate attenuated overburden pressure, and drawing present the horizontal and vertical distribution of formation pore pressure at the same time. Through analyzing, the original formation pore pressure of block G128 in the main development series above jujube V basicly belongs to the normal pressure system, the equivalent density is between 0.95～1.15g/cm3; in the main reservoir where jujube V appears partial abnormal that scope, the overburden pressure attenuation is not that obvious.(2) Establish 3D geological model by collecting block G128 tectonic map, fault data, hierarchical data and well data, etc. On the basis of reservoir porosity, permeability, oil saturation, which are the basic attribute of 3D models, for the first time to add 3D factors such as the original overburden pressure, the initial formation pore pressure and recent attenuated pore pressure. Through profile analysis of geological model, the porosity and permeability of block G128 presents a good correspondence. Affected by sedimentary environment and the reservoir heterogeneity, there is a big difference between the upper and lower or in the same sets of oil on jujube V, and oil is mainly distributed in the upper small high porosity, high permeability layer.(3) Import well field J39-49 of block G128 to create deterministic model, combine dynamic production data to simulate pressure depletion of reservoir. The method of history matching of this numerical simulation is to use a given amount of liquid fit cumulative oil production approach. Adjust the model to make the dynamic basically the same of actual dynamic, and finally simulate the formation pressure curve and stereogram. By curve analysis shows that block G128’s reservoir pressure depletion is around 2MPa, the pressure maintained in good condition; stereogram of a single well analysis shows that the closer the wells, the greater the reservoir pressure depletion.