The methane hydrate (MH) production tests were conducted using the depressurization method in the JOGMEC/NRCan/Aurora Mallik production program in April 2007 and in March 2008. In addition to attaining the first and the only successful methane gas production to the surface from a MH reservoir by depressurization in the world, various data such as wellhead/bottomhole pressure, temperature, gas and water flow rates and the temperature along the casing measured by Distributed Temperature Sensing (DTS) systems were acquired during these tests. The flow rates of gas and water from the reservoir sand face were then estimated by the comprehensive analysis of these data. This paper clarifies the details of the estimation of gas and water flow rates based on these data, for the first time after the 2008 winter test.In 2007, a certain amount of gas and water were produced from a 12 m perforation interval in one of the major MH reservoirs at the Mallik site in Canada, by reducing the bottomhole pressure down to about 7 MPa. However, because of the irregular (onoff) pumping operations due probably to the excessive sand production, the produced gas was not directly delivered to the surface via the tubing, but was accumulated at the top of the casing. Hence, the gas production rate was calculated based on the continuously monitored bottomhole and casing head pressure. Since the produced water was injected into the aquifer located below the MH reservoir, it was impossible to directly measure the water pumping rate. The pumping rate and water production rates were accurately estimated by matching the bottomhole temperature through the numerical simulation using a wellbore model.In 2008, much larger and longer gas production was accomplished with a stepwise reduction of the bottomhole pressure down to about 4.5 MPa, preventing sands from flowing into the wellbore by the screen. In this test, both the gas and water were delivered to the surface, which enables the estimation of the gas and water flow rates from the reservoir sand face as well as liquid level in casing based on the monitored parameters.Investigating the production performances thus estimated, it was inferred what really happened in the reservoir during the tests. These insights must be beneficial for future exploration and development planning for MH resources.

No 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.

The JOGMEC/NRCan/Aurora Mallik gas hydrate production tests were conducted using the depressurization method in April of 2007 and March of 2008. These tests represent the first and so far only successful sustained production in the world of methane gas to surface from a gas hydrate reservoir by depressurization. A variety of data, such as wellhead/bottom-hole pressure and temperature, gas/water flow rates, and temperature along the casing measured by distributed temperature sensing, were acquired during the tests. The flow rates of gas and water from the reservoir sand face during the tests were estimated by comprehensive analysis of these data. Diverse history-matching simulation was then conducted to reproduce these estimated flow rates, using the numerical simulator MH21-HYDRES coded especially for gas hydrate reservoirs. This series of history-matching simulation studies quantitatively clarified the mechanisms of methane hydrate dissociation and production, as well as what had happened in the reservoir during the production tests. This paper describes the procedures and results of a series of these studies, including the analyses of production-test data, numerical modelling and history-matching simulation, which will provide beneficial insights into the mechanisms of methane hydrate dissociation and production for future exploration and development planning for gas hydrate resources.

Methane hydrate MH is being highlighted as next-generation hydrocarbon resources mainly because of its huge in place and cleanness. The Research Consortium for Methane Hydrate Resources in Japan MH21 Research Consortium , which was organized to attain the exploration and exploitation of MH resources, has been implementing a variety of research projects. As part of such research projects, we have been developing a state-of-the-art numerical simulator called MH21-HYDRES' for rigorously predicting MH dissociation and production performances. The main functions of this simulator and the efforts toward improving and verifying this simulator are introduced in this paper. The gas production from MH reservoirs is significantly different from that from conventional oil and gas reservoirs in terms of the mechanism and the phenomena, since 1 MH is a solid, 2 reservoir behaviors are associated with the chemical reactions such as MH dissociation/formation, and 3 reservoir properties, especially permeability, change drastically by MH dissociation. Therefore, it is impossible to predict MH reservoir performances by conventional oil and gas reservoir simulators, which lead to the development of the own numerical simulator specialized for MH reservoirs. Currently MH21-HYDRES can be applied to three-dimensional Cartesian and two-dimensional radial coordinate systems. This simulator can also deal with six components of methane, water, nitrogen, carbon dioxide, methanol and salt, and with five phases of gas, water, ice, MH and precipitated salt. The main features of this simulator are to calculate the kinetics of endothermic dissociation and exothermic formation reactions of MH as well as multi-phase flow behaviors resulting from these reactions. The simulator divides a target reservoir into multiple grid blocks, for which the pressure, temperature, water saturation, methanol and salt mass fractions, etc. are calculated solving the system of discretized non-linear equations for the component mass conservation and the overall energy conservation. To shorten the computational time, it is preferable to reduce the total number of grid blocks and hence to increase the size of grid blocks. On the other hand, larger grid blocks result in more significant numerical errors, which is more serious in a MH simulator than in a conventional oil and gas simulator. To resolve these problems inconsistent with each other, the Dynamic Local Grid Refinement DLGR function was incorporated into the simulator. DLGR enables a shorter computational time without reducing the accuracy of prediction, by allocating fine grid blocks only to the regions of importance where MH is being dissociated/formed at every time step. In addition, we are attempting to parallelize MH21-HYDRES utilizing the published MPI message passing interface and the parallelized solver for a linear equation system. Although the parallelized MH21-HYDRES is still in the prototype stage, using four processors, we could successfully achieve the computational speed that is about three times fa...