Yanan, China
Yanan, China

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Zheng W.,Zaoyuan Road | Dong X.,Zaoyuan Road | Zhang Y.,Zaoyuan Road | Wu B.,Zaoyuan Road
Drilling Fluid and Completion Fluid | Year: 2015

Borehole collapse had always been encountered when drilling the Shiqianfeng and Shihezi formations in Yanchang gas field. Laboratory study has been conducted to determine the mechanism governing the borehole wall instability. By measuring the geo-stress, mechanical characteristics of the rocks in formations where borehole collapse was encountered, mineral composition, and physic-chemical properties of the formations, it was found that the Shiqianfeng and Shihezi formations are composed of hard and brittle rocks, is capable of being dilatant at stresses that are far below the peak stress. Fluctuation of pressure forced the micro fractures near the wellbore to extend and converge, forming an instable high permeability zone. Study found that no high tectonic stress exists in Yanchang gas field, but formation reversion and fracture are quite developed. The formations drilled are in late diagenesis, and the mudstones have high clay content, making them moderate to strong swelling. Drilling fluid used in drilling these formations should have good inhibitive capacity. Low mud weight, less than the density equivalent of collapse pressure of formation, caused the formation to collapse. Long period of time for the borehole to be "empty" (with no drill tools in the hole) led to increasing collapse pressure of the formations, aggravating borehole collapse. Poor sealing and plugging ability of the drilling fluid, which cannot effectively seal and plug micro fractures on the borehole wall, was another cause of borehole collapse. ©, 2015, North China Petroleum Administration Drilling Technology Research Institute. All right reserved.


Liu G.,Zaoyuan Road
Petroleum Refinery Engineering | Year: 2014

Amine-based drilling fluid having high inhibitive and sealing capacities is studied for use in Yanchang Gasfield. In laboratory studies, an amine inhibitor, AI-1, of low cost, is developed. AI-1 has inhibitive capacity similar to that of PEA, and inhibits the yield of bentonite. Hot rolling test and swelling test with shale samples from Liujiagou Formation of Yanchang show that AI-1 has very good inhibitive capacity and minor effect on mud rheology. An amine drilling fluid formulated with AI-1 as inhibitor, modified starch, SPNH and PAC-LV as filter loss reducers, and ZHFD and FT-1 as sealing and plugging agents, has excellent inhibitive capacity, good rheology, low filtration rate and tough mud cake. It has low impairment to reservoir's flow capacity, greater than 90% permeability recovery is obtained with core samples from Shihezi Formation, Shanxi Formation and Benxi Formation of Yanchang. This aminebased fluid has been used in three wells in Yanchang, wiping out borehole instability and mud losses. Gauge hole was obtained and ROP was increased.


Liu G.,Zaoyuan Road | Mao Y.,Zaoyuan Road | Wu G.,Zaoyuan Road
Drilling Fluid and Completion Fluid | Year: 2014

Amine-based drilling fluid having high inhibitive and sealing capacities is studied for use in Yanchang Gasfield. In laboratory studies, an amine inhibitor, AI-1, of low cost, is developed. AI-1 has inhibitive capacity similar to that of PEA, and inhibits the yield of bentonite. Hot rolling test and swelling test with shale samples from Liujiagou Formation of Yanchang show that AI-1 has very good inhibitive capacity and minor effect on mud rheology. An amine drilling fluid formulated with AI-1 as inhibitor, modified starch, SPNH and PAC-LV as filter loss reducers, and ZHFD and FT-1 as sealing and plugging agents, has excellent inhibitive capacity, good rheology, low filtration rate and tough mud cake. It has low impairment to reservoir's flow capacity, greater than 90% permeability recovery is obtained with core samples from Shihezi Formation, Shanxi Formation and Benxi Formation of Yanchang. This amine-based fluid has been used in three wells in Yanchang, wiping out borehole instability and mud losses. Gauge hole was obtained and ROP was increased.

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