Abstract
The southern edge of the Junggar basin has broad exploration potential. However, high-frequency complex drilling accidents in this area lead to the reduction of the average drilling speed and the extension of the drilling cycle. The main geological reason is that this area was affected by the process and developed high and steep geological structure. The nappe formation with a large dip angle and poor stability developed along faults. The major rock type of this E2-3a formation is mud-stone which has strong water sensitivity and can be hydrated and dispersed easily, which leads to the wellbore shrinkage and the borehole collapse. In order to improve the drilling speed in the southern edge of the Junggar basin and accelerate the exploration and development process, the drilling fluids associated with drilling problems in this area were investigated in this paper by combing the geological information and historical drilling records. Because of the special characteristics of this formation, it is concluded that the water-based drilling fluids previously used in this area are not suitable to solve the complex drilling conditions; a high density oil-based drilling fluid system has been developed for this area by conducting studies in the laboratory initially and being tested in the field later. In addition, its rheology, stability and pollution resistance performances were evaluated. Results show that, the rheology, the stability and pollution resistance capacities of the drilling fluid satisfy the drilling requirements. The fluid was applied in well H101 and the results show that the ROP of section 311.1 mm of the well was increased by 763% compared to the wells drilled in the same area and the total drilling time of well H101 was reduced by more than 80%, which was a historic breakthrough of the drilling speed in the southern edge.
Highlights
The southern edge of the Junggar Basin in Xinjiang of China is one of the areas with abundant oil and gas reservoir
Because of the special characteristics of this formation, it is concluded that the water-based drilling fluids previously used in this area are not suitable to solve the complex drilling conditions; a high density oil-based drilling fluid system has been developed for this area by conducting studies in the laboratory initially and being tested in the field later
The fluid was applied in well H101 and the results show that the ROP of section 311.1 mm of the well was increased by 763% compared to the wells drilled in the same area and the total drilling time of well H101 was reduced by more than 80%, which was a historic breakthrough of the drilling speed in the southern edge
Summary
The southern edge of the Junggar Basin in Xinjiang of China is one of the areas with abundant oil and gas reservoir. The southern edge is in the Piedmont of the northern Tianshan Mountain, affected by the tectonic movement and the fold formed in the plane. This area, which has great exploitation potential, was ideal for oil and gas gathering. Affected by the tectonic process, the middle-upper part comes with big dip angles and fault repetition of the old and new strata, which leads to the fragmented formation with poor stability. The lower part of the formation comes with the high stress and abnormal high pressure, the high density drilling fluid is needed to balance the formation pressure during the drilling
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