Oil Gravity Drainage Research Articles

Theoretical studies on the gravity drainage of heavy oil during in‐situ steam heating

AbstractOne concept for the in‐situ production of oil from the tar sands involves the continuous injection of steam into a growing steam‐saturated volume or steam chamber. Steam flow to the boundary of the chamber, condenses and gives up its heat to the surrounding oil sands. The condensate and heated oil flow by gravity to a production well located at the bottom of a chamber and are removed continuously. The well may consist of a horizontal slotted pipe. This paper describes the theory of operation of such a process and an equation is derived which predicts the rate of drainage.

The Gravity Drainage of Steam-heated Heavy Oil to Parallel Horizontal Wells

Introduction In a previous paper, an equation was derived which predicts the rate of drainage of heavy oil around an expanding steam chamber which is above a horizontal production well. The theory was developed for a reservoir of finite height, but infinite extent. In the present paper, the theory is extended to the more practical confined arrangement in which drainage is to a series of parallel wells. Theoretical expressions are derived for the rate of drainage as a function of the main significant variables. The paper also describes scaled experiments carried out using a reservoir model with a transparent side. A series of photographs of this model show the development of the steam chamber with time. The results from the model are compared with the theoretical predictions. INTRODUCTION In a previous paper (Ref. 1), a novel approach to the production of heavy oils was described in which steam was injected continuously into a growing steam chamber which formed above a horizontal production well. In this process, the steam injection rate is controlled so as to maintain the steam pressure within the chamber approximately constant. Steam flows to the edge of the chamber and condenses. This heats the oil which drains from around the walls of the chamber to the production well below. This paper extends the theory developed earlier. A main requirement in the mathematical analysis was that a simple solution was sought. The analysis started from a consideration of a small part of a freely moving interface. Heal was assumed to penetrate beyond the interface by thermal conduction using a constant thermal diffusivity for the reservoir. The interface was assumed to be at steam temperature and the temperature distribution beyond the interface was assumed to be the steady-state distribution corresponding to the instantaneous rate of advance of the interface. The viscosity of the oil was calculated as a function of temperature and then of distance and the total drainage flow was obtained using Darcy"s equation and the gravity driving force. Allowance was made for the fact that the interface was inclined and curved. The differential equations were then integrated over the height of the reservoir and the simple equation (1) which resulted expressed the total rate of drainage. (Equation in Full Paper) In this paper, the theory is extended and modified in two directions:The calculated interface curves are modified so that they remain attached to the production well. This makes allowance for the head required to move oil from the interface horizontally to the well. This is discussed below under the heading TANDRAIN.The theory is modified to allow for the confining effect of adjacent wells. In the previous theory, the interface was allowed to spread horizontally to infinity; in the present treatment, it spreads only to a vertical no-flow boundary located half way to the next adjacent well. TANDRAIN The interface curves which are generated by the original theory rise rapidly and then become asymptotic to the top of the reservoir.

The Gravity Drainage Mechanism

Richard H. Smith, general production superintendent for the Signal Oil and Gas Co., presented the eighth talk in the series on "Elements of Petroleum Production" at a recent meeting of the Pacific Technology Forum. Smith discussed the mechanism of gravity drainage as it affects production from petroleum reservoirs. Smith first defined gravity drainage as differential movement of oil and gas within an oil reservoir caused by density differences such that counterflow is achieved. He then discussed the balance between gravity forces and capillary forces that controls the counterflow of oil and gas in a gravity drainage system; and, on the basis of this discussion, presented an analysis of gravity drainage in oil reservoirs. Characteristics of 12 oil pools were presented to illustrate a method for determining whether or not gravity drainage was a major portion of the producing mechanism for each pool. He then presented methods for detecting gravity drainage early in the life of an oil pool and discussed briefly the necessity for detecting gravity drainage or a lack of gravity drainage before a gas injection program is begun: One of the first field studies that indicated the presence of gravity drainage as a production mechanism was made by H. C. Miller, who studied such pools as Yates, Shuler-Jones and Oklahoma City. He noted that early in the life of these pools reservoir pressure declined rapidly, but that later in the life of the pools pressure declined only slowly although substantial quantities of oil continued to be produced. Miller concluded that this later production was the result of gravity drainage of oil into the wells.