Drilling Fluid Technology for Complex Deep Cambrian Formations in Tarim Basin
The complex Cambrian formations in Tarim Basin exhibit complex geological characteristics such as large depth,ultra-high temperature,ultra-high pressure,complex lithology,fluids,and stress.Prominent issues during drilling include the collapse of fractured dolomite formations,instability of wellbore due to dissolution of thin gypsum layers,drilling fluid contamination,and poor stability of high-temperature drilling fluids.Based on theoretical analysis,strategy for preventing the collapse of fractured formations through"reasonable density support,multi-stage plugging while drilling,and static reinforcement with closed mud,"strategy for avoiding sticking in"unsaturated and low-filtration loss"gypsum-containing dolomite formations,and strategy for controlling high-temperature performance of drilling fluids through"polymer and sulphonation material synergy against temperature"were proposed.Key treatment agents such as high-temperature resistant plugging and collapse prevention agents,high-temperature resistant and salt-resistant polymer filtration reducers,multi-scale wide-size particle plugging and collapse prevention treatment agents,sulphonation treatment agents,and high-temperature resistant and efficient lubricants were used.Through laboratory experiments,SMDP-2 high-temperature resistant and salt-resistant filtration reducer was selected as the optimal agent,and the formulation of plugging and collapse prevention materials was determined.The optimal dosage of SMJH-1 lubricant was identified and high-temperature resistant,strong plugging,and unsaturated saltwater drilling fluid system capable of withstanding temperatures up to 200°C was constructed.This drilling fluid has been applied in three wells including Well QSH1,demonstrating good inhibitory properties,plugging and collapse prevention properties,and high-temperature stability,achieving rapid drilling through complex formations.In Well QSH1,the average daily leakage rate of the Lower Qulitalik and Awatagulik formations decreased by 45.6%compared to adjacent wells,with a borehole enlargement rate of 9.52%,and downhole logging and casing were completed smoothly,reducing drilling time by 30.32%.The research indicates that this drilling fluid technology effectively addresses drilling challenges in complex Cambrian formations in Tarim Basin at temperatures below 200°C,providing technical support for safe and rapid drilling in such formations.
Cambrianfractured formationdolomitewellbore collapseunsaturated salt water drilling fluidTarim Basin
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