Closed Hole Circulation Drilling: Case Study of Drilling a High-Pressure Fractured Reservoir - Tengiz Field, Tengiz, Republic of Kazakhstan

Abstract The drilling of a sour, high-pressure fractured reservoir in the Tengiz field of Kazakhstan displayed complex and hazardous well control situations. While drilling the carbonate reservoir termed Unit 1, multiple fractures were encountered resulting in severe lost circulation followed by hydrocarbon influx into the well-bore. Severe and uncontrollable lost circulation in the target reservoir prompted the use of special practices and equipment; thereby enhancing the safety and efficiency in the development drilling of the field. A rotating control device (RCD) was employed to drill ahead blind (no fluid returns) by pumping a sacrificial fluid (water) down the drillpipe. Simultaneously, a pressurized mud-cap on the annulus with weighted oil based mud OBM controlled hydrocarbon influx. The overall process of pressurized mud-cap drilling will be described by the term Closed Hole Circulation Drilling (CHCD). The successful application of CHCD has resulted in Tengiz well T-7252 being the first well to completely penetrate Unit 1 where lost circulation could not be controlled by conventional methods. After all Unit 1 fractures had been penetrated, a liner was installed to isolate the fractures using the same CHCD well control procedures employed while drilling the interval. This technical paper will describe the process used to successfully plan, develop, and implement the CHCD technique in the Tengiz field.