The rock in deep strata of Wuxia area in Junggar Basin is abrasive and with low drillability. Part of the formation sections with abundant fractures, which leads to mud lose frequently. The exploration progress has been slowed down by low drilling speed and accidents. The exploration department of Xinjiang Oilfield Company preferred underbalanced drilling technology on well F8 and A1 on the basis of feasibility analysis of UBD technology in Permian strata. The applications reduced lose circulation effectively and promote the rate of penetration considerably. Well F8 and A1 used foam and nitrogen as underbalanced drilling circulation medium respectively. The wellbore sizes are 215.9 mm. The rate of penetration in underbalanced drilling sections are quintuple than conventional rotary drilling. It saved more than 20 days in the overall drilling time. The conversions between foam/nitrogen with mud were successfully once only. There was no losing circulation during underbalanced drilling progress. The successful application of underbalanced drilling technology in deep strata of Wuxia area solved the deep drilling speed improved problems entirely. It reduced mud lose and promote drilling speed. The drilling overall time and exploration cost has also been decreased greatly. The innovation application provides a new method for deep drilling speed improved in this area. In the passed drilling, the ROP of advanced cone and PDC bits was nearly 0.65 m/h, and the ROP was no more than 0.92 m/h even with turbodrills and impregnated bits. However, the ROP of underbalanced drilling section has promoted several times than conventional drilling. ROP optimizing was substantial versus direct offset wells that experienced quintuple drilling time through the same formation. With this success, the team has accumulated valuable experience of deep drilling for Junggar Basin.
The candidate wells are tight oil wells and most of the wells in the area have a low recovery rate of fracturing fluid after fracturing treatment. The lithology is glutenite with weak cementation and a high sensitivity tendency. This paper presents the process of sensitivity evaluation and fracturing fluid evaluation. Also, this paper introduces a customized and optimized clay control fracturing fluid wells in a highly sensitive reservoir. Per local national standard, traditional methods of swelling test (ST) and x-ray diffraction (XRD) were employed for qualitative formation cutting analysis. An innovative trial was then developed to evaluate cores quantitatively by water sensitivity. A clay stabilizer was then chosen to be used for the highly sensitive cores and regain permeability testing of the broken fracturing fluid was performed. Based on the analysis and evaluation, a customized treatment design was initiated for the hydraulic fracturing treatment. The qualitative evaluation showed the rock is highly water sensitive and the cores easily collapse because of weak cementation. No flow could be established during traditional core flow tests with brine. The newly developed method used kerosene as the working fluid to prevent the cores from contact with water or brine. The core flow tests resulted in a velocity sensitivity damage rate of 92%, which is considered as highly velocity sensitive. Accordingly, a special clay stabilizer was chosen to be used in the fracturing fluid and the permeability damage of the broken fracturing fluid is only 26.9%(Table 16). Field results have shown that the fracturing fluid recovery rate in treated wells is higher than the area average level and treated wells have significant oil production increase. The innovative clay control fracturing fluid and its field application reduces the influence of water and velocity sensitivity. The customized treatment with special clay stabilizer helps increase the recovery rate of fracturing fluid in reservoirs with severe clay stability and weak cementation issues.
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