Research On Well Type Preference And Fracturing Capacity Of Thick And Low Permeability Gas Reservoirs At Sea

The development of marine low permeability gas reservoir, which contains thick layers, has a variety of different drilling well types. Due to different development technologies and processes for these well types, which can result in different adaptabilities to the stratigraphic characteristics of a same region, the recovery effect in the same area vary from one well type to another. Therefore, it is necessary to select reasonable and effective well type in accordance with different geological and topography conditions as well as investment costs in the development of marine low permeability gas reservoir with thick layers.From the perspective of gas reservoir engineering?drilling technique?economic benefit, the criterion of well type optimization is to effectively improve gas well productivity?to be in line with the requirements of existing technologies?to realize the recovery benefits, respectively. Only meet the requirements of gas reservoir engineering, drilling technique and economic benefit, can we choose reasonable and effective well type for the development of gas reservoir. Based on the background of marine low permeability gas reservoir with thick layers as well as many investigations of existing exploration and development status of such reservoir, this paper analyzed technical characteristics?advantages and disadvantages?existing problems and application effects of different development methods; and then according to technical demands of different development modes, the paper studied the adaptabilities of major development methods on the basis of geology?formation?terrain?economic evaluation, etc.This paper mainly drew the following conclusions:(1) Based on a large number of domestic and foreign literature researches, the application of horizontal well technology to low permeability gas reservoir was preliminarily studied; the characteristics of marine low permeability gas reservoir were summarized; the characteristic parameters of horizontal wells in similar gas field were analyzed and compared, for instance, reservoir thickness, permeability, horizontal segment length, drilling rate, fracturing technology and capacity after fracturing;(2) Establishment of horizontal section formula model for a horizontal well and theoretical fonnula derivation which can obtain pressure drop mode as well as coupling model for horizontal section; and then calculated the horizontal section length via reservoir parameters;(3) Determinations of productivity formula for horizontal well?straight well and inclined well with big angle; stimulations and researches of independent and joint development mode in X region offshore; and then analyses and contrasts of stimulation times for these two different development modes;(4) Based on representative logging data, this paper established single well numerical simulation model for horizontal well?straight well and inclined well with big angle, respectively, and then considered two different development patterns (natural depletion, fracturing)?compared the length of stable production period and cumulative gas production under same production allocation?combined with fracturing investment, feasibility of fracturing was determined in this paper;(5) Through economic benefit evaluations and comparisons of different well types in marine low permeability gas reservoir, well type optimization can be obtained, which is for the development of marine low permeability gas reservoir with thick layers, on the basis of existing equipment and technical conditions at home.The research results in this paper enhances the effectiveness of optimization for well types in marine low permeability gas reservoir, and are significant for scientifically guiding the applications of different well types in such kind of gas reservoir.