RU2537721C1 - Method for development of oil deposits with gas cap and low formation temperature - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention is related to the development of oil deposits with a gas cap, preferably at the initial stage of an oil deposit development. The invention is applied at oil deposits with low formation temperature. The concept of the invention is as follows: wells are drilled in the areas of a gas cap location, cold water is injected to the formation within the gas cap interval in a volume sufficient to reach or maintain the required pressure and temperature conditions in result of cold water injection for the purpose of gas hydrates formation and isolation of the gas cap by these hydrates from the oil part in the deposit. At the next stage the deposit is drilled and oil is produced from the oil area at that maintaining the formation pressure and temperature at a level required for the presence of stable gas hydrates. Upon recovery of reserves from the deposit the oil part formation pressure is decreased or the formation temperature is increased in order to decompose hydrates and to produce associated gas from the gas cap.

EFFECT: reducing a risk of the associated gas breakdown from the gas cap to the producers, increasing the oil recovery factor, reducing th time for the deposit development.

Description

The invention relates to the oil industry and may find application in the development of an oil field with a gas cap, preferably at the initial stage of development of an oil field. The method is applicable to fields with low reservoir temperature.

When developing fields with a gas cap, there is a danger of a gas breakthrough into production wells, as a result of which the oil production rate of the wells decreases, a part of the oil reservoir is blocked, the oil recovery coefficient decreases, and the field development time increases.

A known method of developing an oil reservoir at an early stage, including the selection of oil through production wells, analysis of the properties of reservoir fluids by the reservoir, the boundaries of the oil-water zone and the non-reservoir zone, the conclusion that there are two reservoirs with a qualitative difference in the properties of reservoir fluids, determining the estimated boundary of one reservoir, limiting it along the border of the oil-water zone and the estimated border between the deposits, determining the direction of the extension of the oil reservoir towards the non-reservoir zone, taking into account the direction of the strike oil deposits of the region, the operation of existing wells as production wells with the gradual transfer of some of the wells to injection wells, the formation of the direction of the injection rows, as close as possible to the direction perpendicular to the long axis of the new reservoir, the placement of a new grid of wells in accordance with the newly defined direction of the reservoir, the operation of wells as producers with the gradual transfer of some of the wells to injection wells, a new analysis of the properties of fluids in the reservoir and the boundary of the oil-water zone and the non-reservoir zone , Clarification of new deposits and its border areas [1]. The main disadvantage of this method is the need for a significant number of measures to clarify the development system and the optimal placement of wells.

The closest in technical essence is a method of developing an oil field with a gas cap, including drilling directional injection, production and gas wells, pumping water into the oil reservoir through the injection wells, taking oil through production wells and pumping associated petroleum gas into the gas cap above the oil reservoir through gas wells [2]. The disadvantages of the method are the low coefficient of oil recovery due to the formation of rims with high residual oil reserves, the formation of gas cones in the bottomhole formation zone of the producing wells, as well as the increased risk of a breakthrough of gas from the gas cap into the producing wells.

The aim of the invention is the isolation of associated petroleum gas of the gas cap to reduce the risk of breakthroughs into production wells.

This goal is achieved by pumping cold water into the gas cap to form gas hydrates that block the gas cap from the oil zone. The formation of a hydration screen separating the gas cap from the oil zone occurs due to the interaction of associated petroleum gas from the gas cap with cold water under conditions of low reservoir temperature and sufficient reservoir pressure. In addition, due to the injection of water into the reservoir, an increase in reservoir pressure also occurs, which facilitates hydrate formation.

The technical results achieved by using the present invention are:

reducing the risk of breakthrough associated petroleum gas from the gas cap into production wells;

increase in oil recovery ratio;

reduction of field development time.

To implement the invention, wells are drilled in the gas cap regions. Next, cold water is injected into the reservoir in the interval of the gas cap in a volume sufficient to block gas cap from the oil part of the reservoir with gas hydrates. For the formation of hydrates, it is necessary to maintain or achieve the necessary thermobaric conditions in the reservoir by injecting water, determined by laboratory methods and depending on the composition of associated petroleum gas from the gas cap. After the formation of gas hydrates that block the gas cap from the oil zone of the reservoir, the field is drilled and oil is extracted from the oil zone. An important condition is the maintenance of reservoir pressure and temperature in the reservoir at a level necessary for the stable existence of gas hydrates. After depletion of the oil reserves of the reservoir, reservoir pressure is reduced or reservoir temperature is increased to decompose hydrates and produce associated petroleum gas from the gas cap.

Information sources

1. RF patent No. 2096606, ЕВВ 43/30, 43/20, 11/20/1997.

2. Shchelkachev V.N. The state of oil production and the introduction of enhanced oil recovery methods abroad. Series "Oilfield business", M.: VNIIONG, 1985, p.19-26.

Claims (1)

         A method of developing oil fields with a gas cap and low formation temperature, including drilling wells in areas where the gas cap is located, pumping cold water into the reservoir in the interval of the gas cap in a volume sufficient to achieve or maintain the required thermobaric conditions in the reservoir by injecting cold water to form gas hydrates and their blocking of the gas cap from the oil part of the reservoir, subsequent drilling of the field and oil production from the oil zone while maintaining reservoir pressure and temperature in the reservoir at the level necessary for the stable existence of gas hydrates, the implementation after the development of reserves of the oil part of the reservoir to reduce reservoir pressure or increase reservoir temperature for decomposition of gas hydrates and production of associated petroleum gas from the gas cap.