Abstract

Sebei Gas Field in Qinghai is the fourth largest gas field in China. The reservoirs here are of unconsolidated Quaternary siltstones and pelitic siltstones, alternating gas and water layers and with serious sand production. The grain size of the sands is very fine, so it is very difficult to realize sand control, a cosmopolitan puzzle. We have succeeded in applying a series of techniques of comprehensive sand control with fiber-complex high-pressure packing but without any screen pipe. The technology includes the reservoir pretreatment, the fiber-complex technique and the high pressure packing. As for the reservoir pretreatment, the soft fibers, of which the branched chains are with positive electrical charges, are used to adsorb the fine silty sand particles to form big aggregations for sand stabilization. As for the fiber-complex technique, the 3-dimensional reticular fiber and resin-coated sand complex are adopted for sand retention. As for the high pressure packing, the formation is not fractured while the fiber composites are packed to form screen pipe-like barrier around the cement sheath to perform sand control without any screen pipe used, eliminate any damage to the near wellbore zone and increase the gas bleeding area. This technique can achieve the dual purpose of sand control and production stimulation. This technique system had been applied in Well Se 7–1–4 in Sebei Gas Field with remarkable results achieved. After such sand control treatment, the output without sand production increased on average to 2.1 times of the output before. This paper presents mainly the relevant theory, experimental study, operation design and field application of the fine silty sand control technique using the fiber-complex high-pressure packing without any screen pipe.

Design

Sebei Gas Field in Qinghai is the fourth largest gas field in China. The reservoirs in this gas field are mainly of Quaternary siltstones and pelitic siltstones, undercompaction, poor diagenism and loose cementation. The reservoirs possess characteristics of high clay content, high shale content, high degree of mineralization, strong sensitivity, alternating gas and water layers as well as serious sand production. The produced sands are fine silty sands with grain size of 0.03–0.07mm, so the conventional sand control techniques are ineffective or work poorly, confronting with tremendous difficulty in sand control. In the past ten years, several oil service companies at home and abroad had been invited to apply some technologies such as mechanical, chemical and fracturing sand control in the gas field, but no expected results had been obtained[1]. Thus, the gas field production can only depend on the pressure control technique, which can only achieve approximately 30% of the productivity and greatly reduced the production of the gas wells.

By targeting the specific characteristics of the reservoirs in Sebei Gas Field, research has been done in two steps by using a technology called the sand control technology with fiber-complex high-pressure packing. Firstly, to deal with the reservoirs' strong sensitivity and fine silty sands, we have used a cation radical branch chained soft fiber treatment fluid for the formation pretreatment. Secondly, because of the alternating gas and water layers and to prevent from fracturing the water layer, research was done to apply the high-pressure packing technology, without fracturing the formation, to fill in the 3-dimensional reticular-structured complex of fiber and resin-coated sand around the cement sheath to generate a sand retention barrier that has high diverting capability[2,3].

A pilot test of this technology has been completed in Gas Well Se 7–1–4 in Sebei Gas Field recently. After the sand control treatment, the gas production with no sand production has increased to 2.1 times of that before. The application of this sand control technique has achieved remarkable economical benefits in the gas field.

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