【摘要】：實際鉆井過程中,井眼通常會存在一定程度擴徑而不會出現(xiàn)與井眼失穩(wěn)相關(guān)的井下復(fù)雜�，F(xiàn)有坍塌壓力計算模型不允許任何程度的井壁破壞,計算得到維持井壁穩(wěn)定所需的最小井內(nèi)壓力過于保守。井壁穩(wěn)定并非井眼完整,維持鉆井過程中井眼完整需要的井內(nèi)壓力過高,甚至超過地層破裂壓力,會造成鉆井液漏失。由于不同井斜角的井眼能承受的破壞程度不同,定向井井眼需要承受上覆地層壓力,進而井壁穩(wěn)定問題較直井更加突出。因此需要建立新的定向井坍塌壓力計算模型,允許井眼存在一定程度的井壁崩落,以降低鉆井液密度的同時維持井壁穩(wěn)定。 本文利用多孔線彈性巖石力學(xué)理論,分別結(jié)合Mohr-Coulomb準(zhǔn)則、Mogi-Coulomb準(zhǔn)則、修正Lade準(zhǔn)則、Drucker-Prager外接圓及內(nèi)切圓準(zhǔn)則,建立了基于井壁崩落的定向井坍塌壓力的計算模型。該模型可計算定向井井眼在不同破壞程度時所需的井內(nèi)壓力,即坍塌壓力,并根據(jù)坍塌壓力優(yōu)化定向井井眼軌跡。地應(yīng)力是鉆井液密度及井眼軌跡設(shè)計的重要參數(shù),利用井壁崩落確定最大水平地應(yīng)力大小的方法已得到廣泛的運用,然而相應(yīng)的模型僅適用于直井。盡管貝克休斯GMI軟件可以利用任意定向井的井壁崩落確定最大水平地應(yīng)力的大小,但并未有文獻提出其方法。在建立定向井坍塌壓力計算模型的過程中,本文找出了利用定向井井壁崩落寬度確定最大水平地應(yīng)力的方法。 根據(jù)已建立的定向井坍塌壓力計算模型,利用Visual C#.NET開發(fā)了基于井壁崩落的定向井坍塌壓力計算軟件。該軟件可以利用定向井的井壁崩落寬度計算最大水平地應(yīng)力的大小,根據(jù)Mohr-Coulomb準(zhǔn)則和修正Lade準(zhǔn)則計算的結(jié)果與GMI軟件基本一致。結(jié)合Mohr-Coulomb準(zhǔn)則、修正Lade準(zhǔn)則、Drucker-Prager外接圓及內(nèi)切圓準(zhǔn)則,利用該軟件計算了允許井壁崩落和不允許井壁崩落的定向井坍塌壓力,計算結(jié)果與GMI軟件基本一致甚至完全一致。 基于井壁崩落的定向井坍塌壓力計算軟件與GMI軟件的計算結(jié)果對比表明,二者相當(dāng)接近甚至完全一致,允許井壁崩落可以顯著地降低定向井坍塌壓力。因此,可以得出結(jié)論：本文提出的利用定向井井壁崩落寬度來確定最大水平地應(yīng)力的方法正確可靠,開發(fā)的軟件可用于計算最大水平地應(yīng)力和定向井坍塌壓力。
[Abstract]:In the actual drilling process, the borehole will usually have a certain degree of diameter expansion without any downhole complexity associated with borehole instability. The existing collapse pressure calculation model does not allow any damage to the wellbore, and the minimum in-well pressure needed to maintain the stability of the borehole is too conservative. The wellbore stability is not complete. The drilling fluid leakage will be caused by the high pressure in the borehole which is needed to maintain the borehole integrity or even exceed the formation fracture pressure. The directional borehole needs to bear the overlying formation pressure because of the different damage degree of the borehole with different inclined angle, and the problem of wellbore stability is more prominent than that of the straight well. Therefore, it is necessary to establish a new model for calculating the collapse pressure of directional wells to allow a certain degree of wellbore caving, so as to reduce the density of drilling fluid and maintain the wellbore stability at the same time. Based on the theory of porous linear elastic rock mechanics and Mohr-Coulomb criterion Mogi-Coulomb criterion and modified Lade criterion Drucker-Prager outer circle and internal tangent circle criterion, a model for calculating collapse pressure of directional well based on wellbore caving is established in this paper. The model can be used to calculate the in-well pressure, i.e. the collapse pressure, which is required by the directional wellbore under different failure degrees, and to optimize the directional wellbore trajectory according to the collapse pressure. The in-situ stress is an important parameter of drilling fluid density and borehole trajectory design. The method of determining the maximum horizontal stress by wellbore caving has been widely used, but the corresponding model is only suitable for vertical wells. Although the baker Hughes GMI software can be used to determine the maximum horizontal stress by using the sidewall caving of an arbitrary directional well, no method has been proposed in the literature. In the course of establishing a model for calculating the collapse pressure of directional wells, a method for determining the maximum horizontal ground stress by using the sidewall caving width of directional wells is found in this paper. Based on the established collapse pressure calculation model of directional well, the collapse pressure calculation software of directional well based on wellbore caving is developed by using Visual C#.NET. The software can be used to calculate the maximum horizontal stress by using the wellbore caving width of the directional well. The results calculated by the Mohr-Coulomb criterion and the modified Lade criterion are in good agreement with the GMI software. Combined with Mohr-Coulomb criterion and modified Lade criterion Drucker-Prager circumscribed circle and internal tangent circle criterion, the collapse pressure of directional well with and without wall caving is calculated by using this software. The calculated results are consistent with or even completely consistent with GMI software. The calculation results of directional well collapse pressure based on wellbore caving and GMI software show that both of them are quite close to or even consistent with each other, and allowing sidewall caving can significantly reduce the collapse pressure of directional well. Therefore, it can be concluded that the method proposed in this paper to determine the maximum horizontal ground stress by using the sidewall caving width of the directional well is correct and reliable, and the developed software can be used to calculate the maximum horizontal ground stress and the collapse pressure of the directional well.
【學(xué)位授予單位】：西南石油大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TE21

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