Abstract

Taking temperature as a dividing criterion, the investigations and applications of organosilicon drilling fluid system (ODFS) on the fifth largest gas field in China, Qingshen gas field, have experienced three phases from 180 °C, 200 °C to current 220 °C. In the first two phases, ODFS has been successfully used for drilling 48 deep wells.

In the third phase, the high temperature (HT) deep gas well in Qingshen gas field, Xushen 22, was drilled to 5320 m (17454 ft) with bottom hole temperature of 220 °C (428 °F). Since high temperature can cause clay dispersion and deactivation, as well as the degradation and crosslink of organic compound, the severe high temperature drilling environment posed a host of technical challenges and environmental issues. The difficulty of drilling operations was further increased by the extremely hard and brittle formation, because such formation potentially increases the risk of hole instability. Therefore, for drilling the HT deep gas well Xushen 22, a new type of organosilicon drilling fluid system with improved thermal stability and hole stability was required. Based on the mechanism study on different HT additives, we formulated a high-performance ODFS-III whose properties were examined through a full-scale laboratory tests. Finally, we applied the ODFS-III on well Xushen 22.

The results obtained from the field application show that ODFS-III has good thermal stability and special rheology, and also provides good shale stabilization, which meet the hydraulics and hole-cleaning demands of deep-well operations.

Introduction

In order to produce deep oil and gas reserves, we need to face up to many technical challenges. One of the key challenges is the designing of drilling uid for HT/HP deep wells. In deep wells, the oil-based mud has been proven to be robust in high-temperature environments, but the use of oil-based mud is prevented by environmental regulations, in many areas. Besides the negative impact to environment (Francis et al. 1995), some other drawbacks of oil-based mud such as the relative high cost and influence on logging interpretation also limit its application. Desai et al. (2006) stated that the main reason for operators to apply water-based drilling fluid was the risk and costs of using oil-based mud in highly sensitive environment. Downs et al. (2006) pointed out that, oil-based mud (OBM) can absorb a large amount of gas, which is potentially an unsafe factor for well control.

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