Application of horizontal well to gas production from a hydrate reservoir with free gas and high irreducible water

Abstract

Due to the ever-increasing energy demand, the study of gas production from marine methane hydrate attracts intensive interest around the world. Vertical wells were adopted in most of the previous production tests, although horizontal well might be with significant advantage over vertical well in production performance. To evaluate the gas production performance from a high irreducible water saturated hydrate reservoir with free gas underlain using horizontal well, a multilayered hydrate reservoir model is established, of which all the sediment layers are with high saturation of irreducible water and a free gas layer occurs beneath the hydrate zone. Gas production performances on single horizontal well and two paralleled horizontal wells are investigated. The simulation results obtained show that gas production with horizontal well can yield a high gas production rate, especially at the early stage of production with the contribution of free gas. A horizontal well located at the bottom of the hydrate layer is recommended, because it can not only extract free gas in gas production but also induce more dissociation of hydrate. When two paralleled horizontal well-configuration is applied, the middle and bottom well pattern can generate a synergistic effect that accelerates hydrate dissociation and reduces water production. The sensitivity analyses of free gas saturation and irreducible water saturation show that either of the two factors can result in a high gas-to-water ratio.