Study On Hydration Control Method Of Hard And Brittle Shale

The hard-brittle shale formation has always been a troublesome geological body where complicated accidents happened frequently during drilling for oil and gas. According to statistics, more than90%borehole collapse occurs in the shale formation, and hard-brittle shale accounts for2/3. The instability of hard brittle shale wellbore is significantly caused by hard brittle shale hydration, which induced rock structure damage and mechanical properties degradation. And that is restriction to drilling, completion or other engineering activities in such formation. Hence researchers focus on hydration mechanism, control methods and related fields gradually.This article analyzed mineralogy composition and microstructure charateristics of the hard-brittle shale form Longmaxi formation. Based on these analysis, hydration features and correlative mechanism of clay mineral containing in hard-brittle shale has been studied by several ways. The hydration characteristics of hard-brittle shale have been studied from macroscopic and microcosmic point at the same time. Combining these studies, hydration mechanism of hard-brittle shale was discussed afterwards. On the basis of mechanism, the hydrate inhibitor for hard brittle shale was synthesized to study chemical control method for shale hydration.The studying suggested that brittle shale contains quartz, feldspar and other brittle minerals mainly (50-80%). The clay content ranges from15to40%, which was mainly comprised by low swelling clay illite with contents over60%. Illite/smectite formation and chlorite are the minor constituents of clay minerals in shale. According to SEM analysis, the there are considerable micron-sized pore throats and micro-fractures in the shale; It was also found that illite particle surface shows strong physical and chemical activity. Although its volume expansion is very small, the swelling stress is large and the hydration rate is very fast; The swelling characteristic of the Na-MMT interlayer spacing (d001) was analyzed. It was found that due to its huge volume in aqueous solution, the polymer molecules hardly had remarkable effect on the expansion of the interlayer spacing, on the other hand, the electrolytes, especially KC1could inhibit the expansion of the interlayer spacing, and the interactive between cationic and the internal space of the crystal layer was the key factor that influenced the expansion of interlayer spacing.The research on the hydration behavior of hard-brittle shale shows that the main character of brittle shale was the generation, expansion and connectivity of the secondary fractures under the influence of water.Combining the studies mentioned above, the hydration mechanism of hard-brittle shale was discussed, and it can be concluded that "spontaneous imbibitions","swelling stress","interlayer expansion" are the three keys to control the hydration of hard-brittle shale.At present, various methods was used to control shale hydration. According to understanding of hydrate mechanism of shale, this article chose chemical method to inhibit its hydration. Based on acrylamide (AM),1-allyl-1-methylimidazolium chloride (MAC), acrylic polyethers(APEG) and2-acrylamido-2-methyl propane sulfonic acid(AMPS) to synthesize two different water-soluble polymer hydrate inhibitor of hard brittle shale:poly (AM/APEG/MAC) and poly (AM/APEG/MAC/AMPS). Meanwhile, the inhibit effect of two polymers was investigated. The results showed that with the effect of poly (AM/APEG/MAC) and poly (AM/APEG/MAC/AMPS), illite hydration can be slowed down remarkably and its swelling stress can be reduced by49%and52%. It has also found that these two copolymers poly (AM/APEG/MAC) and poly (AM/APEG/MAC/AMPS), blending with KC1, can improve the retention of indentation hardness from35%to58%and69%respectively.This thesis was based on the Key research project of national natural science funds: Basic Research of Low cost, Efficient Drilling and Completion Technology in Shale Gas Development(U1262209).