【摘要】：水力壓裂的目的在于增加地層的裂縫,但壓裂也可能導(dǎo)致壓裂液沿套管井的水泥環(huán)及其周圍空間流動,俗稱竄槽。竄槽會使儲層之間相互污染,導(dǎo)致試井時油層出水等現(xiàn)象,并且影響壓裂的順利進(jìn)行。本文研究水力壓裂引起竄槽的條件,并考慮避免竄槽的對策。論文分別按強(qiáng)度理論和斷裂力學(xué)方法研究了壓裂過程中引起套管井失去水力封隔效能的兩類通道的形成機(jī)制。這兩類通道是:套管井水泥膠結(jié)良好,但水泥環(huán)因強(qiáng)度不足而發(fā)生脆性破壞,形成竄槽通道;水泥與套管之間(第一界面)或者水泥與地層之間(第二界面)在壓裂之前就存在微小流體間隙,壓裂過程中微間隙擴(kuò)展而形成竄槽通道。針對界面膠結(jié)完好的套管井段,利用三維有限元模擬了水泥環(huán)脆性破壞導(dǎo)致的竄槽行為。分析了水壓作用下套管井射孔附近區(qū)域的應(yīng)力狀態(tài),計算了使地層或水泥環(huán)破壞的臨界注水壓力,并研究了不同介質(zhì)參數(shù)、射孔條件和地應(yīng)力條件下水泥環(huán)的抗竄能力。研究表明,用低楊氏模量、高泊松比的水泥進(jìn)行固井,可以有效防止水泥環(huán)竄槽。在低楊氏模量、高泊松比的地層進(jìn)行壓裂會導(dǎo)致水泥環(huán)竄槽的發(fā)生。射孔條件以及地應(yīng)力的偏應(yīng)力對水泥環(huán)竄槽機(jī)制影響不大。而地應(yīng)力的靜水壓會影響水泥環(huán)的水力封隔能力。本文將界面流體間隙視為含水界面裂紋,研究了套管井界面裂紋在水壓作用下的擴(kuò)展。壓裂過程中界面裂紋的擴(kuò)展會導(dǎo)致竄槽發(fā)生。本文分別針對第一界面和第二界面存在裂紋的套管井,利用內(nèi)聚力單元模擬界面的力學(xué)行為,分析了水泥屬性、地層屬性和地應(yīng)力對界面竄槽的影響。結(jié)果表明,高楊氏模量、高泊松比的水泥會提高固井界面的抗竄能力。而在地層楊氏模量低、泊松比低的井段進(jìn)行壓裂,界面不易竄槽。水平地應(yīng)力的提高可提高界面的抗竄能力,但垂直地應(yīng)力的變化對界面抗竄能力影響很小。本文考慮綜合兩種竄槽機(jī)制,給出避免壓裂過程中發(fā)生竄槽的方案。結(jié)果表明,固井時應(yīng)采用高泊松比的水泥,而水泥楊氏模量應(yīng)在一個合理的范圍內(nèi);選擇進(jìn)行壓裂的地層,其泊松比應(yīng)盡量低,而楊氏模量不能過高或過低;應(yīng)盡量選擇水平地應(yīng)力低而垂直地應(yīng)力高的位置進(jìn)行壓裂。
[Abstract]:The purpose of hydraulic fracturing is to increase the formation fracture, but fracturing may also lead to the flow of fracturing fluid along the cement ring of casing well and its surrounding space, commonly known as channeling channel. Channeling will pollute each other between reservoirs and lead to reservoir effluent during well testing and affect the smooth fracturing. In this paper, the conditions of channeling caused by hydraulic fracturing are studied, and the countermeasures to avoid channeling are considered. According to strength theory and fracture mechanics method, this paper studies the formation mechanism of two kinds of channels which cause casing well to lose its hydraulic sealing efficiency during fracturing. The two kinds of channels are: cement cementation is good in casing well, but the cement ring is brittle and broken because of insufficient strength, forming channeling channel; Between cement and casing (the first interface) or between cement and formation (the second interface) before fracturing there is a tiny fluid gap. The channeling behavior caused by brittle failure of cement ring is simulated by three dimensional finite element method for casing section with well-cemented interface. The stress state in the area near perforation of casing well under water pressure is analyzed, the critical water injection pressure that causes formation or cement ring failure is calculated, and the anti-channeling ability of cement ring under different medium parameters, perforation conditions and in-situ stress conditions is studied. The results show that cement cementing with low Young's modulus and high Poisson's ratio can effectively prevent cement ring channeling. Fracturing in low Young's modulus and high Poisson ratio will lead to cement ring channeling. The perforation condition and the deflection stress of in-situ stress have little effect on the channeling mechanism of cement ring. The hydrostatic pressure of in-situ stress will affect the hydraulic sealing capacity of cement ring. In this paper, the interfacial fluid gap is regarded as the water-bearing interface crack, and the propagation of the interfacial crack in casing well under the action of water pressure is studied. During fracturing, the growth of interfacial crack will lead to channeling. In this paper, for the casing wells with cracks at the first and second interfaces, the effects of cement properties, formation properties and in-situ stresses on the interfacial channeling are analyzed by using cohesive force unit to simulate the mechanical behavior of the interface. The results show that cement with high Young's modulus and high Poisson's ratio can improve the anti-channeling ability of cementing interface. But in the formation where Young's modulus is low and Poisson's ratio is low, the interface is not easy to be channeled. The anti-channeling ability of the interface can be improved by the increase of horizontal in-situ stress, but the change of vertical in-situ stress has little effect on the anti-channeling ability of the interface. In this paper, two kinds of channeling mechanisms are considered, and the scheme of avoiding channeling during fracturing is given. The results show that the cement with high Poisson's ratio should be used in cementing, and the Young's modulus of cement should be within a reasonable range, the Poisson's ratio should be as low as possible in the fracturing formation, and the Young's modulus should not be too high or too low. Fracturing should be carried out in a position where horizontal stress is low and vertical stress is high.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TE256

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本文編號：2233051