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- ISSN: 2333-2581
- Modern Environmental Science and Engineering
Innovative Technologies for Drilling Fluid Loss Control in Deep Wells with Complex Pressure System in Central Asia Oilfield
Abstract: Reservoirs at Mingebrak Basin in Uzbekistan are characterized by big burial depth (5200-6500m), high temperature (150-200℃), high pressure (pressure coefficient 2.08-2.41), high salt content (220000 mg/l), and high H2S content (5~6%) in the formation fluid. The Musgothic formation is especially complex because it contains different pressure systems. Leakage and blowout are easy to occur during well drilling and the average drilling period is 732 days. The data of well drilling history have been analyzed and the causes of the long drilling period have been detected. The results showed that the drilling problems in the Musgothic formation was the main cause of the non-drilling time because leakage and overflow occurred frequently and time was consumed in dealing with leakage and overflow. Three methods have been taken to conquer the drilling problems: finding out the setting positions and improving the wellbore structure; selecting the organic salt drilling fluid and optimizing the formula of it through experiments; developing different lost circulation materials to bridge different types of leakage. Leakage prevention and control technologies have been worked out through analysis and experiments. Firstly, the mudstone at the top of Musgothic and the high-pressure formation at bottom of Musgothic were taken as setting positions respectively and the wellbore structure was improved from three-hole structure to four-hole or five-hole structure. Secondly, an organic salt drilling fluid formula with temperature resistance of 180℃, salt contamination resistance of 30% NaCl and 1% gypsum, and 93.48% recycle rate was developed. Thirdly, three types of loss control materials: return loss control materials, fracture loss control materials, and permeable leakage control materials were developed to deal with different types of formation leakage. The three methods, five-hole wellbore structure, high temperature organic salt drilling fluid and 840 m3 loss control materials have been successfully used in an exploration well M15 in Mingebrak Oilfield, and the drilling period was only 390 days, only about a half of the average drilling period in this area. The study of the mud loss prevention and control technologies of this paper is significant for reducing the drilling period in Mingebrak Oilfield, Uzbekistan. Their successful application in well M15 set a good example for safe and fast drilling of deep wells in this oilfield and the technologies will be popularized for application in other wells of this area.
Key words: HT/HP, high salt, high H2S, deep well, mud losses
