Abstract

Sebei Gas Field is located in the northeast of Caidam Basin, Qinghai, China. Its main pay-zone is unconsolidation Quaternary fine-silty and dirty sandstones with serious sand production. Grain size of the sand is very fine, about 0.04–0.07mm, so sand control is very difficult. In past ten years, many sand control methods (such as mechanical, chemical and frac-pack sand control) have been applied; however, expectant effect had not been achieved. Condisering the conditions of Sebai Gas Field, we succeed in applying a series of technique of comprehensive sand control with fiber -resin coated sand. The technique adopts formation pretreatment, clear brine-based VES (viscoelastic surfactant) fracture fluid as sand carrier, special glass fibers and resin-coated sand complex for fracture pack stabilization and enhanced proppant transport, frac-pack and TSO (tip screen out) for increasing productivity, bypassing near well bore damage, interconnecting multiple sandstone layers and decreasing fluid velocities in the formation to reduce fines production. This combined rehabilitation technique enabled screenless sand control completion, allowing low cost rehabilitation of plugged or failed sand screens and the development of any numbers of gas layers which otherwise could not be drained with conventional sand control technologies.

The technique was exercised in well Se 3–18; the results proved to be remarkable. Before sand control, serious sand production begins at 4.5×104m3; after sand control, sand production cannot be found at 91200 m3/d. Up to now, the well has been produced for nearly one year with stable gas production at 10×104m3 and no more sand production. This paper presents lab study, operation design, field operation and result analysis about the sand control technique.

Introduction

Sebei Gas Field of Caidam Basin is the fourth largest gas field in China with reserves of about 3000×108m3. Burial depth varies greatly from 540m to 1740m and the gas-bearing layer is thick. The reservoir lithology mainly consists of siltstone, pelitic siltstone and fine sandstone. The single layers are quite thin, varying from 0.8m to 9.4m and the interlayers are also thin. There are a number of layers (from 47 to 68 layers). As a whole, the reservoir is of thin, numerous, isolated, and complex characteristics. The gas and water is of complex relation and the gas and water layers are interlacing. The diagenesis and consolidation of the under compaction reservoir are both poor. Shale content is 40%–60% and the mineralization is 15–17 104ppm. The permeability of the reservoir ranges from 100×10–3 μm2 to 1000×10–3μm2 with a maximum of 8436.4×10–3μm2, a minimum of 0.1×10–3μm2 and an average value of 571.72×10–3μm2. The maximum porosity is 44.2% while the minimum is 10.2% and the average value is 31.77%. Moreover, the receptance of the reservoir is strong and sand production is very serious. Therefore, most of the wells can only produce gas with controlled pressure difference. The production of three-fourths gas wells is restricted under 5.0×104m3/d and the exertion of the off-take potential of the gas wells is dramatically restrained. The siltstone produced by reservoir is very fine with a granularity of 0.04–0.07mm; therefore, the conventional sand control techniques are of basically no efficiency or very poor efficiency and it is very difficult to control sand, which greatly depress the efficient development of the oil field.[1]

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