Research on Safe Drilling Technology for Ultra Deep Ultrahigh Pressure Saltwater Zones in Piedmont Area, Kuche

Wells drilled in the piedmont area in Kyche, Xinjiang have to penetrate thick salt and gypsum formations, which have complex geology, ultrahigh pressure saltwater with poor distribution patterns in length and breadth, highly varied formation pressures that are difficult to predict. Drilling fluid properties inevitably become deteriorated when high pressure saltwater cut is encountered. The deterioration of drilling fluid properties in turn results in frequent blowout, lost circulation, or pipe sticking, significantly affecting the progress of drilling operation. To resolve these problems, the entrapment nature of the high pressure saltwater and previous drilling practices were analyzed based on the drilling behavior in high pressure saltwater drilling. In laboratory study, simulating experiments were conducted to determine the limits of saltwater invasion to drilling fluid. Based on the research, a new technique has been developed to minimize the effects of high pressure saltwater. In this technique, the high pressure saltwater is allowed to go into the drilling fluid in annular space in a controlled manner by regulating choke valves and the flow rate of drilling fluid. Each time the volume of water allowed into the well should not exceed 10% of the volume of the annular space. Many times of saltwater draining reduces formation pressure. In this way, the downhole troubles resulted from saltwater invasion can be minimized, thus mitigating the drilling difficulties resulted from the piedmont ultra-deep ultra-high pressure saltwater. Field application of this technique has shown that, using sound method to drain saltwater under controlled pressure is able to reduce saltwater formation pressure. A balance point between water kick and mud loss should be found to ensure the safety of well control.