Potential on joint development of three-gas reservoirs in the Qiongdongnan Basin

Abstract

<p>Gas hydrates are typically found in the fine-grained sediments with low abundance and strong heterogeneity in the northern South China Sea. To date, although numerous gas hydrate reservoirs have been discovered, commercial exploitation remains highly challenging. Previous studies show that the Qiongdongnan Basin exhibits coexistence of gas hydrates, shallow gas and deep gas reservoirs. The hydrate-bound gases are a mixture of thermogenic and biogenic gas, mainly sourced from the granite buried hill reservoir, central canyon channel of the Lingshui Depression and the Yacheng Formation. In this study, we described a new development concept termed ��Three-gas Joint Development�� (TJD), to elucidate the simultaneous exploitation of these three gas reservoirs. Based on the distribution of three-gas reservoirs, three different TJD plans are proposed. If the relative distance between three-gas reservoirs does not exceeds the extension limit, a single production platform is capable of exploiting all three-gas reservoirs. A vertical well is suggested if the deep gas reservoir lies directly below the gas hydrates and shallow gas. Otherwise, multilateral well should be used to exploit different gas reservoirs with various branches in a main wellbore. However, several key issues remain unsolved. Numerical simulation of TJD should be conducted to evaluate interlayer interference and productivity. Efficient sand control and wellbore stability techniques, such as frac-packing and high-performance drilling fluids, are recommended when drilling unconsolidated sediments. Once these key technologies are overcome, TJD can provide a feasible approach for the commercial development of gas hydrates.</p>