A Feasibility Study of Producing Natural Gas from Subsea Hydrates with Horizontal Snake Wells

Abstract

This study focuses on technical feasibility of producing natural gas from offshore gas hydrate deposits using a new technique called horizontal snake wells (HSW). This paper addresses engineering and well productivity issues for the new technique. Coiled tubing string is proposed to drill HSW in gas hydrate reservoirs for increasing well productivity and reducing wellbore collapse problems. A new analytical model was derived to predict of maximum achievable wellbore length (MAWL) based on the theory of buckling failure. Furui's equation for gas reservoirs was used for predicting the initial well productivity at the MAWL. Gas lift method is proposed to remove water for achieving a constant bottom hole pressure that is slightly below the hydrate dissociation pressure. Gas production forecast was made on the basis of material balance. Net present value (NPV) method is employed to perform economics analysis. A gas hydrate reservoir in the South China Sea was taken as an example to investigate the feasibility of producing natural gas from gas hydrate deposits using the HSW technique. The new analytical model gave the MAWL under extreme well friction conditions prior to buckling failure of coiled tubing. Furui's equation predicted commercial well productivity at the MAWL, depending on the loop separation of the HSW. If the bottom pressure is maintained with gas lift technique at a constant level slightly lower than the hydrate dissociation pressure to prevent wellbore collapse, material balance forecasted high NPV of HSW. It is concluded that the HSW is a feasible technique for economically producing natural gas from offshore gas hydrate deposits. This paper presents a novel method called HSW for producing natural gas from offshore gas hydrate deposits. It also demonstrates how to evaluate the productivity and thus economics of the HSW.

Mathematical Modeling of the Dynamic Temperature Profile in Geothermal-Energy-Heated Natural Gas Hydrate Reservoirs

“…Field pilots test gas well productivity in NGH reservoirs [7,8]. While these studies continue to deepen people's understanding of properties of NGH reservoirs and challenges in field operations during natural gas extraction from the NGH sediments, efforts are shifting from being stagnant with the documented huge reserve amount [9] to more relevant technical and economic studies on NGH pay zone potentials, gas well productivity, and gas well construction techniques [10][11][12][13].…”

“…These two issues arose because of reducing wellbore pressure in depressurization and thermal stimulation for improving well productivity. Although some novel ideas have been proposed to solve these problems, including the use of radial lateral wells [28], frac-packed wells [13] and horizontal snake wells [10,12], they have not been tested in the field.…”

Mathematical Modeling of Heat Transfer from Geothermal Reservoirs to Gas Hydrate Reservoirs

“…These two issues arose because of reducing wellbore pressure in depressurization and thermal stimulation for improving well productivity. Although some novel ideas have been proposed to solve these problems, including the use of radial lateral wells [28], frac-packed wells [13] and horizontal snake wells [10][12], they have not been tested in the field.…”

A priori assessment of long‐term productivity of frac‐packed wells for producing natural gas from marine gas hydrate reservoirs

“…To reduce production drawdown and mitigate the associated wellbore collapse and sand production problems while still increasing well productivity, new well configurations were proposed recently, which include horizontal snake wells, radial‐lateral wells 14 , and frac‐packed wells. According to the studies of Wan et al, 15 the horizontal snake well technology can increase the well production rate from 50 MMscf per day to 65 MMscf per day, but it can be very difficult to place snake wellbores in marine gas hydrate reservoirs due to their unconsolidated nature and shallow depth of the gas hydrate zones. Zhang et al 14 proposed to drill radial‐lateral wells in gas hydrate reservoirs for enhancing gas production rate.…”