This invention relates to the oil and gas industry, more specifically, to the development of heavy oil and asphaltic bitumen deposits.
The permanent growth of hydrocarbon prices and the inevitable depletion of light oil resources have recently caused increasing attention to the development of heavy oil and asphaltic bitumen deposits. Among the existing methods of developing high viscosity hydrocarbon deposits (e.g. mining, solvent injection etc.), thermal methods (hot water injection, thermal-steam well treatment, thermal-steam formation treatment etc.) are known for their high oil recovery and withdrawal rate.
Known is a thermal-steam gravity treatment method (SAGD) which is currently one of the most efficient heavy oil and asphaltic bitumen deposit development methods (Butler R.: “Thermal Recovery of Oil and Bitumen”, Prentice-Hall Inc., New-Jersey, 1991, Butler R., “Horizontal Wells for the Recovery of Oil, Gas and Bitumen”, Petroleum Society of Canadian Institute of Mining, Metallurgy and Petroleum, 1994). This method implies creation of a high-temperature ‘steam chamber’ in the formation by injecting steam into the top horizontal well and recovering oil from the bottom well. In spite of its worldwide use, this deposit development method requires further improvement, i.e. by increasing the oil-to-steam ration and providing steam chamber development control.
One way to increase the efficiency of SAGD is process control and adjustment based on permanent temperature monitoring. This is achieved by installing distributed temperature measurement systems in the wells. One of the main problems related to thermal development methods (e.g. steam assisted gravity drainage) is steam (hot water, steam/gas mixture) breakthrough towards the production well via highly permeable interlayers. This greatly reduces the heat carrier usage efficiency and causes possible loss of downhole equipment. Steam breakthrough response requires repair-and-renewal operations that in turn cause loss of time and possible halting of the project. This problem is especially important for the steam assisted gravity development method due to the small distances (5-10 m) between the production and the injection wells.
Known is a method of active temperature measurements of running wells (RU 2194160). The known invention relates to the geophysical study of running wells and can be used for the determination of annulus fluid flow intervals. The technical result of the known invention is increasing the authenticity and uniqueness of well and annulus fluid flow determination. This is achieved by performing temperature vs time measurements and comparing the resultant temperature vs time profiles during well operation. The temperature vs time profiles are recorded before and after short-term local heating of the casing string within the presumed fluid flow interval. Fluid flow parameters are judged about from temperature growth rate.
Known is a method of determining the permeability of geological areas (RU 2045082). The method comprises creating a pressure pulse in the injection well and performing differential acoustic logging and temperature measurements in several measurement wells. Temperature is measured with centered and non-centered gages. The resultant functions are used to make judgment on the permeability inhomogeneity of the string/cement sheath/formation/well system, and thermometer readings are used to determine the permeability vector direction. Disadvantages of this method are as follows:
The object of the method suggested herein is to broaden its application area and provide the possibility of quantifying the filtration parameters of rocks along the well bore thereby increasing heat carrier usage efficiency and reducing equipment losses during deposit development.
This object is achieved by using the new sequence of measurements and steps and applying an adequate mathematical model of the process.
Advantages of the method suggested herein are the possibility of characterizing high viscosity oil and bitumen saturated rocks and using standard measurement tools. Moreover, the sequence of steps suggested herein does not interrupt the process flow of thermal development works.
The method of determining the filtration properties of rocks is implemented as follows:
The invention will be exemplified below with drawings where
The method suggested herein requires distributed temperature measurements over the whole length of the portion of interest at the preliminary heating stage. At that development stage (
To solve the reverse task, this method provides an analytical model satisfying the following properties and having the following boundary conditions:
The position of the oil/water boundary can be determined using the following equation:
where
The value of the parameter cq≈0.5÷1.5 can be assessed from numeric simulation/field experiments to allow for the following specific features that can hardly be incorporated into a purely analytical model:
Thus, the oil/water boundary radius is determined by the following parameters:
The steam/water boundary position is determined by the energy and weight balance equations and can be found as follows:
is the steam condensation weight rate,
is the maximum condensation rate, ρw is the density of water, φ is the formation porosity, λfw is the heat conductivity of the water-saturated reservoir, cw is the heat capacity of water, cs is the heat capacity of steam, α is the thermal diffusivity of the formation, L is the heat of evaporation, tc is the duration of injection and Tc is the steam condensation temperature.
The temperature profile at the steam injection stage is as follows:
Temperature restoration after steam circulation stoppage can be described with a simple conductive heat exchange model not allowing for phase transitions.
Example of filtration properties (permeability K) distribution assessment based on temperature restoration rate measurements is shown in
Thus, the method of determining the filtration properties of rocks suggested herein allows quantification of the permeability profile along the well bore at an early stage of steam-assisted gravity drainage or another heat-assisted well development method. The resultant permeability profile can be used for the preventive isolation of highly permeable formations before the initiation of the main development stage and allows avoiding steam breakthrough towards the production well. The permeability profile along the whole well bore length is determined by measuring the non-steady-state thermal field with a distributed temperature measurement system.
Number | Date | Country | Kind |
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2006104892 | Feb 2006 | RU | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/RU2007/000056 | 2/6/2007 | WO | 00 | 7/29/2010 |