Well Management Under Uncertain Gas or Water Oil Ratios

Abstract

Abstract In the daily operation of an oil production system, it is often required to choke back some of the oil production wells to ensure that the processing capacity is not over-utilized. When the capacity of some processing resource is over-utilized, wells having large ratios between the consumption of the resource and the oil production rate are choked back. When there is free processing capacity, the chokes of the wells having small ratios are opened. Often, the gas or water oil ratios (derived from the water cuts) are used as such ratios. These ratios are uncertain. This paper proposes to use information about the uncertainties of the gas or water oil ratios to find the order of opening and closing the wells to maximize the expected total oil production rate from the wells. In a computational study based on field data, it is found that the order may be different from the one found using the expected value of the gas or water oil ratios and that the expected total oil production rate was increased by 10.1 % for this particular case. Introduction In the daily operation of an oil production system, operators may use various means of optimization to maximize the total oil production rate. For example, Lo and Holden [1] proposed a linear program to maximize the total oil production rate of an oil production system having a processing facility constrained by maximum total gas, water, and liquid production rates. The method assumed that the oil potential for each well was independent of the oil potentials of the other wells (independent wells). This is typically true if the wells do not share long flow lines. For offshore oil production systems, so-called platform wells often satisfies this assumption because the production manifold (a blending point) is placed on the processing platform itself close to the wellheads, and not on the seabed. For such platform wells, the pressure drop in the shared piping between the production manifold and the production separator may be regarded as constant because of the short distance and typically large diameters of the piping used. Furthermore, the method assumed that the wells do not experience gas or water coning. Gas lifted wells are in general not handled by the method. The proposed linear program [1] is shown next using a modified notation. The goal is to maximize the total oil production rate Furthermore, the oil production rate from each well must be nonnegative, where is the gas oil ratio and is the water oil ratio. For simplicity, will be used to denote the liquid oil ratio. Liquid is defined as oil and water.