C. Shah Kabir

A Study of Multiphase Flow Behavior in Vertical Wells

This paper presents a physical mode for predicting flow pattern, void fraction, and pressure drop during multiphase flow in vertical wells. The hydrodynamic conditions giving rise to various flow patterns are first analyzed. The method for predicting void fraction and pressure drop is then developed. In the development of the equations for pressure gradient, the contribution of the static head, frictional loss, and kinetic energy loss are examined. Laboratory data from various sources show excellent agreement with the model.

Predicting multiphase flow behavior in a deviated well

In deviated wells of an offshore producing environment, flow of two- or three - phase mixtures are invariably encountered. While large number of investigators have studied vertical multiphase flow behavior, there are few studies, often entirely empirical, that deal with deviated well systems. The main objective of this work is to present a model that predicts both flow regime and pressure gradient in a deviated wellbore. In modeling flow pattern transition and void fraction, an approach similar to that for vertical flow is taken; that is, four principal flow regimes are recognized - bubbly, slug, churn and annular.

Predicting Liquid Gradient in a Pumping-Well Annulus

This work proposes a hydrodynamic model for estimating gas void fraction, f/sub g/, in the bubbly and slug flow regimes. The model is developed from experimental work, involving an air/water system, and from theoretical arguments. The proposed model suggests that prediction of f/sub g/, and hence the bottomhole pressure (BHP), is dependent on such variables as tubing-to-casing-diameter ratio, densities of gas and liquid, and surface tension. Available correlations do not include these variables as flexible inputs for a given system. Computation on a field example indicates that slug flow is the most dominant flow mechanism near the top of liquid column at the earliest times of a buildup test. As buildup progresses, transition from slug to bubbly flow occurs in the entire liquid column. Beyond the afterflow-dominated period, the effect of bubbly flow diminishes as gas flow becomes negligibly small. Comparisons of BHPs are made with the proposed and available correlations. Because the proposed model predicts f/sub g/ between these of the Godbey-Dimon and Podio et al. correlations, BHP is predicted accordingly.

A New Model for Two-Phase Oil/Water Flow: Production Log Interpretation nd Tubular Calculations

This work presents the results of an experimental and theoretical investigation of two-phase oil/water flow behavior in vertical pipes. Bubbly flow is observed to be the predominant flow pattern, although at high flow rates, slug flow as noted. The proposed method, developed from the drift-flux principle, is validated by experimental data and those obtained from other sources. Limited study indicates the proposed methods superiority over others available in the literature. This work further shows the error involved when oil/water flow behavior is predicted by homogeneous, gas/liquid, and constant-slip models. Application of the model for production log interpretation is also documented.

Simplified Wellbore Flow Modeling in Gas-Condensate Systems

Predicting long-term reservoir performance with realistic wellbore models is fraught with uncertainty because of the complexity of two-phase flow. Even a calibrated two-phase-flow model departs from its expected performance trend when changes in flow conditions occur. The full-length paper explores the possibility of using simplified approaches to computing bottomhole pressure (BHP) from wellhead pressure (WHP), measured rates, gravity of producing fluids, and tubular dimensions. Statistical results from BHP computations on three independent data sets comprising 167 gas/condensate-well tests show that the homogeneous model compares quite favorably with mechanistic two-phase-flow models.

Production Strategy for Thin-Oil Columns in Saturated Reservoirs

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.