Water based drilling fluid technology developed for the salt-gypsum bed in Well ZQ2 of the Zhongqiu Block

The Zhongqiu Block is the key block for the productivity construction of 30 million tons in the Tarim Oilfield. The salt-gypsum beds in the piedmont wells of the Tarim Oilfield are geologically complex and oil based drilling fluid is mostly used there. And oil based drilling fluid is also used in the salt-gypsum bed of Well ZQ1. There are low-pressure layers in the Neogene Suweiyi Formation, so circulation loss happens in the process of drilling. As a result, the success rate of circulation loss control by oil based drilling fluid is low and it takes over 60 days. In order to effectively solve the problems of oil based drilling fluid, e.g. blocking and sticking in salt-gypsum beds, low success rate of circulation loss control and high cost, it is determined to apply a set of water based drilling fluid technology to the high-pressure salt-gypsum beds of Jidike Formation and the low-pressure thief zones of Suweiyi Formation in Well ZQ2. By applying the water based drilling fluid technology to the salt-gypsum beds in Well ZQ2, the hard control of the rheological property of drilling fluid and the fluid-loss well building property caused by the salt, gypsum and mud contamination in the Jidike Formation is solved effectively. By virtue of the active circulation loss control technology, it drills through the low-pressure thief zones of Suweiyi Formation smoothly. And the phenomenon of inter-salt “soft mudstone” blocking the choke line doesn’t occur, the performance of the drilling fluid is steady and the borehole is unrestricted. This technology provides a new and feasible idea of drilling fluid technology for speeding up the productivity construction of 30 million tons in the Tarim Oilfield.