Production Strategy for Thin-Oil Columns in Saturated Reservoirs

Abstract

Summary Maximizing oil recovery in thin and ultrathin (<30 ft) oil columns is a challenge because of coning or cresting of unwanted fluids, regardless of well orientation. Significant oil is left behind above the well completion even for horizontal wells when bottom- or edge-water invasion occurs. Two depletion strategies may be enacted to improve recovery of the remaining oil. In the first option, a conventional horizontal is completed below the gas/oil contact (GOC). Once the well waters out, the well is recompleted in the gas zone. Completion occurs either at the crest for a small gas-cap reservoir or at the GOC, inducing reverse cone, for reservoirs with thick-gas columns. Alternatively, one can skip the initial oil completion, where gas disposition is a nonissue. Gravity-stable flooding is required to maximize reserves. Extensive flow simulations in multiple, history-matched models have shown that the proposed strategy improves recovery significantly. Two field examples are presented to demonstrate the usefulness of the proposed method. Using multivariate regression, simple correlations were developed for quick screening of the proposed approach. Experimental design formed the backbone of a parametric study involving various reservoir, fluid, and process variables. We tested and validated the correlations with independent sets of experimental and published field data.

A New Simulation Grid Type is Demonstrated for the Giant Troll Oil and Gas Field

“…The two papers (Hsiu-Hsyong 1998) and (Kabir, Agamini et al 2008) shows the advantages of a horizontally oriented grid to model long horizontal wells in thin oil rim reservoirs. It was shown that with a horizontal grid the well path can be represented exactly at its position, while in a high resolution stratigraphic grid the well has an error in the well path with undulating well paths and fluid contacts.…”

Study on the Reasonable Development Method of Gas Cap Reservoir

“…If crude oil enters gas cap, large amount of oil will be wasted and oil recovery will be influenced. Vo [9], [10] and Kabir [11] pointed out that the key concern is therefore obtaining economic and optimal operations despite the gas and water coning effects that could confine production below commercial rates and hinder recovery. Therefore, coordinated development of gas cap and oil ring has been an ideal way to recover resources in gas-cap reservoirs, Kuppe [12] have confirmed it by considering concurrent gas and oil production from the Virginia Hills Belloy field.…”

Horizontal simulation grids as alternative to structure-based grids for thin oil-zone problems: a comparison study on a Troll segment

“…300 m water depth, and is operated by Statoil. It is primarily a gas field, but also contains a thin oil zone with thickness varying from zero to 26 m. The use of horizontal wells has resulted in a successful recovery of this oil zone, which initially was regarded as challenging to produce due to coning and cusping of both water and gas-typical for thin oil zone production [4,7,9,13,14].…”

“…Only a part of the vertical section, including the oil leg, is shown in (confidential) internal reports. During the last few decades, such grids have been used in different contexts and with apparent success, e.g., Hsu [6] and Kabir et al [7]. However, all these models were used as ad hoc tools, and no attempts were made to assess the quality of the horizontal grid models versus traditional geo-grids.…”