Researches Of Percolation Flow Theory And Deliverability Calculation Method For Horizontal Well

Horizontal well technology has got rapid development in recent years and it was popular in whole petroleum industry increasingly. Horizontal well was widely used in thin layer reservoir, naturally fractured reservoir, fault-block reservoir as well as those oil reservoir with gas or water coning and those gas reservoir with bottom water coning. Moreover, horizontal well has played an more and more important role in the exploitation of heavy oil reservoir, water flooding reservoir and those reservoir with other EOR measures. Nowadays, there are many complicated problems need to be researched in the aspects of seepage theory and productivity calculation of horizontal well. This dissertation makes horizontal well and symmetric multibranch horizontal wells as research object, according to reservoir characteristics and the seepage process of horizontal well, using multidisciplinary knowledges comprehensively including reservoir geology, reservoir seepage theory, point source function, Green function, conformal transformation, partial differential equation and computational mathematics et al, then researches theory and method suitable for describing seepage process and productivity calculation of horizontal well. Main research achievements are as follows:(1) On the basis of source function theory researches, transient seepage theory and pressure response characteristics of horizontal well was researched. The differences between line source model and bar model of horizontal well were compared and the influences of diversified issues on the dynamic pressure curves were researched. For the horizontal well in the reservoir with fault, the distance and angle between horizontal well and fault were researched through model solving and type-curve plotting. For symmetric multibranch horizontal wells, the influences of branch numbers, dimensionless total well-bore length and branch interferences on the pressure response were researched.(2)Flow distribution characteristics of horizontal well under infinite-conductivity and finite-conductivity conditions were calculated. Under infinite-conductivity conditions, when there is no fault in the reservoir, the flow distribution displays symmetric U-type distribution characteristics when flow is stable. When there is an angle between horizontal well and the fault, the flow distribution displays asymmetric U-type distribution characteristics when flow is stable. For symmetric multibranch horizontal wells, because of branch interferences, the flow distribution displays asymmetric U-type distribution and even monotonic distribution characteristics. Branch interferences increased with branch numbers. Under finite-conductivity conditions, the flow distribution also displays asymmetric U-type distribution characteristics with bigger inflow in the heel end than in the toe end when flow is stable. This is because the wellbore pressure in the heel end is the lowest and it has the biggest pressure drop and wellbore inflow.(3)Horizontal well productivity equation of Borisov's , Joshi's , Giger's and Renard-Dupuy's formulae were analyzed comprehensively, and then their differences and similarities were compared. 3-D analytical productivity equation of horizontal well in infinite-acting reservoir with sealed boundary was derived. For the problem of Joshi's formula withoutπin the denominator of vertical seepage resistance term and the treatment of eccentricity as well as the differences between 2-D and 3-D seepage flow field, corresponding improvement method was proposed.(4) Horizontal gas well model considering well-bore structure parameters, turbulent flow under high-speed non-Darcy flow and start-up pressure gradient was established and solved. Binomial deliverability equation describing horizontal gas well was derived. Deliverability of horizontal and vertical well was compared. The influences of start-up pressure gradient and non-Darcy flow on the deliverability of horizontal gas well was researched. The research results had important guiding significance for field application of horizontal gas well productivity analysis.(5)On the basis of previous researches, universal pseudo-steady state productivity equation of horizontal well was researched and the influences of diversified issues on the productivity were analysed. The universal pseudo-steady state productivity equation not only describes horizontal well productivity under both uniform-flux and uniform-pressure wellbore conditions with unified form, but also describes fracture and horizontal well productivity with unified form. It also included and enlarged classical pseudo-steady state productivity equation of Babu-Odeh's and Kuchuk's. On the basis of universal pseudo-steady state productivity equation, naturally fractured horizontal well productivity equation with complex seepage mechanisms different from Genliang Guo's was deduced. Combined with reservoir geological characteristics, the new formula can be used to research the influences of fracture length, fracture density and fracture azimuth on naturally fractured horizontal well productivity.(6) On the basis of theory researches for the productivity of horizontal well, corresponding formulae were applied in Mis Oilfield in Iran actually. Field application results indicated that modified and improved horizontal well productivity formulae in the dissertation had good accuracy and they could be popularly applied.