Well-test analysis for gas hydrate reservoirs: examination of parameters suggested by conventional analysis for the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well

Abstract

In the Mallik 2002 Gas Hydrate Production Research Well Program, formation tests with a Modular Formation Dynamics Tester (MDT)TM tool were conducted and the test results were analyzed using conventional pressure-transient test-analysis methods. The reliability of the reservoir-parameter estimates, however, is uncertain because of the abrupt change in gas hydrate saturation associated with gas hydrate dissociation during the tests. To investigate the applicability of these methods, the bottomhole-pressure responses during MDT tests in the hypothetical and actual gas hydrate zones were predicted using a numerical simulator and then analyzed by conventional test-analysis methods. This study revealed that the conventional methods might indicate the average effective permeability over the area of gas hydrate dissociation, and that they might accurately suggest the radius of gas hydrate dissociation only when applying appropriate multiphase-fluid properties and production rates to the cases with high gas hydrate saturation.

Use of formation pressure test results over a hydrate interval for long-term production forecasting at the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope: Implications of uncertainties

“…This is because the shut-in period is devoid of rate fluctuations suffered by a typical flow period. Kurihara et al (2005Kurihara et al ( , 2008 have demonstrated the application of conventional welltest analysis techniques to analysis of MDT tests in hydrate reservoirs and has explored its limitations. We matched the pressure of the first shut-in period by using the FAST WellTest software package of Fekete that employs an analytical solution of the diffusivity equation with various boundary conditions.…”

Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Simulation-Based Evaluation of Technology and Potential

“…The long-term predictions of production indicated the advantage of depressurization (over thermal stimulation) as a viable method for hydrate dissociation and commercial gas production, and further demonstrated the superiority of methods combining depressurization and thermal stimulation (Moridis et al, 2005b;Kurihara et al, 2005c). The substantial differences in the long-term predictions of the models were not unexpected (given the short duration of the experiment and the almost chaotic behavior of gas wells immediately after the initiation of production), and served to underscore the need for longer-term tests.…”

Challenges, Uncertainties, and Issues Facing Gas Production From Gas-Hydrate Deposits

“…Theoretical developments on well testing of GH reservoirs have received some attention over the past few years. In one of such developments, Kurihara et al (2005) examined the applicability of conventional PTA techniques to interpretation of MDT results in hydrate reservoirs. They simulated flow and shut-in periods similar to those at the Mallik 2002 test, and then applied the conventional PTA techniques for analysis of the synthetically generated pressures.…”

“…The results indicated that the effective permeability found from application of the conventional PTA techniques, was in close agreement with an average effective permeability over the dissociation zone. In their comprehensive work, Kurihara et al (2005) examined the validity of the assumptions used in conventional PTA techniques. These are discussed under "Theoretical Developments.…”

“…(Hancock et al 2005b). Kurihara et al (2005) used a gas-hydrate simulator to analyze one of the MDT tests. The results indicated that the effective permeability found from application of the conventional PTA techniques, was in close agreement with an average effective permeability over the dissociation zone.…”