A possibility of gas extraction from a gas-hydrate massif by means of warm water circulation through a system of wells is demonstrated. A technological scheme and a theoretical model of this process are proposed.Introduction. Modern geological surveys predict that bottom sediments in seas and oceans contain large amounts of hydrocarbon gases in the form of solid gas-hydrate deposits (approximately 98% of gas hydrates are located in the ocean, and only 2% are located on land in permafrost regions [1,2]). Gas-hydrate resources are estimated as (2800-25,000) · 10 12 m 3 [3, 4], and potential resources of methane in gas hydrates can reach 2 · 10 16 m 3 [2-4]. A natural gas hydrate with a volume of 1 m 3 contains up to 180 m 3 of gas and 0.78 m 3 of water [3]. In seas and oceans, gas hydrates are encountered at a depth of 300-400 to 1000-1200 m and more [1,3]. They saturate the upper layer of bottom sediments and occupy approximately 10-20% of the total volume of the latter [3, 4]. Gas-hydrate accumulations were found in many areas of the World Ocean and also on a significant portion of the bottom area of Lake Baikal [5]. The problem of well drilling in a gas-hydrate massif was considered in [6]. Extraction of gas from gas-hydrate massifs seems to be possible by means of their deliberate melting. In this case, warmer water from the subsurface layers can be used as a heat source. In the present paper, we consider the problem of gas washout from a gas hydrate with the use of circulation of warm water through the system of gas production. Figure 1 shows a possible technological scheme of the process of gas washout from a gas-hydrate massif, where the gas-production system consists of two coaxial cylindrical vertical channels (wells). The inner well is designed to transport the heat-carrying agent (warm water) to the open section of the well surrounded by the gas-hydrate massif (bottomhole). Moving upward over the bottomhole, which is a coaxial channel between the walls of the inner well and the massif surrounding the well, the heat-carrying agent washes the gas hydrate out. In this case, the gas and, in addition, water join the upward flow on the section 0 < z < z op owing to gas-hydrate decomposition, and then this two-phase flow passes to the cased layer (z op < z < z cl ).Let us consider the regime of well operation with the pressure p i 0 and temperature T i 0 at the entrance of the inner well and also the pressure p e at the exit of the outer well being maintained constant.1. Constitutive Equations. Let the gas-hydrate massif have a constant temperature T h0 far from the well. As the temperature of water near the sea bottom is approximately 4 • C, we assume in our calculations that T h0 = 4 • C (T h0 = 277 K). Let p h0 = p s (T h0 ) be the equilibrium pressure corresponding to the initial temperature T h0 (at T = T h0 and p = p h0 , the gas hydrate can be in the equilibrium state with its decomposition products, i.e., with water and gas). The equilibrium pressure for the methane gas hydrate at this temperature is p ...

We consider the specifics of decomposition of gas hydrates under thermal and depressive action on a porous medium completely filled with a solid hydrate in the initial condition. The existence of volumetric-expansion zones, in which the hydrate coexists in equilibrium with water and gas, is shown to be possible in high-permeable porous media. The self-similar problems of hydrate decomposition upon depression and heating are studied. Ii is shown that there are solutions according to which hydrate decomposition can occur both on the surface of phase transitions and in the volumetric region. We note that, in the first case, decomposition is possible without heat supply to a medium and even with heat removal.At present, great theoretical and practical interest in studying gas hydrates in porous media has arisen due to the fact that many technological processes occurring in the gas, petroleum, and chemical industry are accompanied by the formation of gas hydrates; deposits of the hydrates of natural gases can occur in porous strata. Many theoretical and experimental investigations of gas hydrates are directed to the development of effective methods of preventing their formation in the extraction, transportation, and treatment of gases.Some aspects of gas-hydrate decomposition in a porous medium completely filled with a hydrate in the initial state were studied in [1-4]. In addition, as shown in [5, 6], decomposition of hydrates that do not completely occupy a porous medium in the initial state is possible in the volumetric zone if a solid hydrate coexists with the decomposition products (gas and water).In this paper, within the framework of self-similar solutions, we consider the specifics of gas-hydrate decomposition under thermal and depressive action on a porous medium completely filled with a solid hydrate in the initial state.1. We consider filtration processes in a porous medium completely filled with a solid hydrate in the initial state. In describing decomposition processes, the following assumptions are usually adopted: the skeleton of a porous medium, a hydrate, and water are incompressible and immobile, the porosity m is constant, and the gas is calorically perfect:Ps, PA, Pl, m = const, pg = Here p0 and vi (i = s, h, l, 9) are the densities and velocities of the phases, p and T are the pressure and the temperature, m is the porosity, and P~ is a gas constant; the subscripts s, h, l, and g refer to the porous-medium, hydrate, fluid, and gas parameters, respectively.For the volumetric contents of the phases c~i ( Fig. 1), we have = 1 -m, = mv, = -v)s , = m(1 -as +ah +al+ag = 1, Sg +SI = i,

Considerable attention has recently been given to the dissociation of hydrates in porous media [1][2][3][4][5][6][7][8]. This paper is devoted to some aspects of the depression-induced dissociation of hydrates completely filling a porous volume in the initial state. Criteria are proposed for parameters of the system where a hydrate is dissociable in the volume zone.1. Fundamental Assumption. Let us consider hydrodynamic and thermophysical processes that occur in porous media during dissociation of hydrates. The system of equations describing these processes has the most general form for a three-phkse region [4], where a solid hydrate and the products of its dissociation [liquid (water) and gas] are present. For the subsequent consideration we assume that: 1) the gas, liquid, solid hydrate, and porous medium have the same temperature at each point, 2) in addition, the porous medium skeleton, the hydrate, and water are incompressible, 3) the porosity is constant, and the gas is calorifically perfect:where p0 (i = s, h, g, l) is the true density, p is the pressure, T is the temperature, R is the gas constant, and m is the porosity. Hereafter the subscripts s, h,g, and l mean that a given parameter belongs to the porous medium skeleton, hydrate, gas, and water, respectively. The porous medium skeleton and the hydrate are immovable (Vs = Vh = 0). The presence of liquid vapors in the gas phase and the gas solubility in the liquid as well as diffusion in the hydrate are neglected. The hydrate is a two-component system having mass concentration of gLs g (mass concentration of the liquid 1 -g). We will neglect diffusion in the hydrate. 2. Fundamental Equations. Taking into account the above assumptions, we write the mass conservation equations for gas and water as follows:where v is the hydrate saturation, m(1 -v) is the "quick" mobile porosity, i.e., a portion of the porous medium volume filled with mobile phases --liquid and gas, Sg and St are the gas and water saturation, respectively, vi (i = gO is the velocity of the phases. For the gas and liquid filtration we use the Darcy law:where k, Ki are the coefficients of absolute permeability and relative phase permeability, respectively, and gi (i = g, l) is the dynamic viscosity. The heat supply equation for the system under consideration, with the Institute of Multiphase System Mechanics, Russian Academy of Sciences, Siberian Division, Tyumen' 625000.

The paper considers the experience of huge mature field development optimization by the example of oil Field Y in the Western Siberia. The approach for automation selection the prospective wells for workover program for the multi-formation field was developed. The automated waterflooding optimization was constructed to increase the sweep efficiency and to balance the injection values by wells. This approach has a significant potential to minimize time expenditures for routine operations, and enables improvement of field development strategies quality. The field development based on secondary recovery methods like workovers, drilling and waterflooding optimization for the field Y (secondary recovery) allowed increasing recovery factor to some degree. For significant increase of recovery the enhancement oil recovery program (tertiary recovery) was prepared.

Реɜюмe The paper presents assisted history matching methods for the preparation and modification of the simulation model parameters (absolute permeability, relative permeability, etc.)). The proposed approaches allow both to speed up the history matching process and improve the accuracy of the simulation results.