天然气水合物储层仿生井壁稳定剂研制及其作用机理

Preparation and mechanism of biomimetic wellbore stabilizer for natural gas hydrate reservoirs

针对南海天然气水合物弱胶结泥质疏松砂岩储层井壁坍塌、失稳难题,本文从模仿贻贝邻苯二酚基团水下粘附机理的思路出发,利用具有成膜性能的聚乙烯醇(PVA)和富含邻苯二酚和邻苯三酚基团的单宁酸(TA)复配,研制了一种能够在水下环境提高井壁稳定性的钻井液固壁剂—仿生强化井壁稳定剂(JBWDJ)。从主动提高粘土矿物颗粒间胶结强度、抑制粘土水化分散、膨胀和稳定水合物构型3个方面强化储层稳定。实验结果表明:JBWDJ浸泡16 h后的岩心土块保持形状完整且具有一定抗压强度,而被清水、聚丙烯酰胺、聚胺抑制剂等溶液处理后的岩心土块均呈散砂状;与未处理岩心相比,JBWDJ可将人造岩心抗压强度提高2.01倍;SiO2微球修饰的原子力探针与5%JBWDJ的粘附力达2314 nN;3%JBWDJ的水溶液处理后的页岩岩屑滚动回收率为80.85%,与清水(48.4%)、聚合物固壁剂(52.35%)和氯化钾(26.3%)溶液处理后的岩屑相比,可显著提高岩屑回收率;含3%JBWDJ的钻井液体系岩心膨胀高度仅为0.9 mm,与不含JBWDJ钻井液体系浸泡处理后岩心土块膨胀高度相比,可将膨胀高度降低50%。流变测试和储层保护实验评价表明,该JBWDJ具有较好的流变性和一定的储层保护能力。透射扫描电镜(TEM)、红外光谱、扫描电镜(SEM)和能谱元素(EDS)等微观机理分析表征阐述了JBWDJ固壁的作用机理。该JBWDJ通过氢键作用构建了网状结构,吸附在岩心颗粒表面,增强了粘土矿物颗粒间的胶结,并在表面形成致密的仿生膜。且具有较好的抑制粘土水化膨胀、分散的效果,从而实现提高岩心抗压强度,强化储层稳定的目的。同时原位拉曼光谱对比分析表明JBWDJ不改变I型甲烷水合物的结构。通过上述力学性能测试和微观机理表征可得出,JBWDJ可为保障水合物储层井壁稳定提供新材料。

A new drilling fluid additive-biomimetic strengthen wellbore stabilizer(JBWDJ)was prepared to solve the issue of wellbore collapse and instability in weakly cemented argillaceous unconsolidated sandstone natural gas hydrate reservoirs in the South China Sea.JBWDJ was developed by imitating the adhesion mechanism of mussel catechol groups underwater environ-ment in this study.Polyvinyl alcohol(PVA)with the property of film-forming and tannic acid(TA)rich in catechol and pyrogallol groups were used based on hydrogen bond.It enhanced hydrate reservoir stability from three aspects:actively improving the bonding strength between clay mineral particles,inhibiting clay hydration dispersion and expansion,and stabilizing hydrate con-figuration.The experiment results showed that the core soil blocks soaked in JBWDJ for 16 hours remain complete in shape and have a certain compressive strength,while treated with solutions including water,polyacrylamide,and polyamine inhibitors are all in a loose sand shape.The compressive strength of the artificial core treated by 3%JBWDJ increased by 2.01 times compared with untreated core samples.Additionally,the adhesion force between atomic force microscope(AFM)probe modified by SiO2 microsphere and 5%JBWDJ reached 2314 nN.Shale cuttings treated with 3%JBWDJ had a rolling recovery rate of 80.85%,which can significantly improve the recovery rate of rock cuttings compared with rock cuttings treated by clean water(48.4%),polymer wellbore stabilizer(52.35%),and potassium chloride(26.3%).The core expansion height of the drilling fluid containing 3%JBWDJ is only 0.9 mm,compared with the core soil block expansion height treated by the drilling fluid system without JBWDJ,the expansion height can be reduced by 50%.Rheological testing and reservoir protection experimental evaluation show that the JBWDJ has good rheological properties and certain reservoir protection capabilities.Microscopic analyses including transmission electron microscopy(TEM),infrared spectroscopy,scanning electron microscopy(SEM),and energy dispersive spectroscopy(EDS)revealed the mechanism of JBWDJ.It is mainly to build a network structure through hydrogen bonding,adsorb on the surface of the rock,enhance the bonding between clay mineral particles,and form a dense biomimetic film on the surface.Meanwhile,it has a good effect on inhibiting the hydration expansion and dispersion of clay,thereby achieving the goal of improving the compressive strength of rock cores and strengthening reservoir stability.Furthermore,in-situ Raman spectroscopy comparative analysis showed that JBWDJ has no impact on the structure of type I methane hydrates.Hopefully,through the above mechanical performance testing and microscopic mechanism characterization,it can provide new materials for ensuring the stability of hydrate reservoir wellbore.