The diffusion coefficient (D) of gases in heavy oils is an important mass transfer parameter to model and design gas injection processes for oil recovery. The pressure‐decay technique (PDT) is one of the widely used experimental methods available to infer this coefficient. PDT records the declining gas phase pressure resulting from the diffusion of gas into heavy oil inside a pressure/volume/temperature (PVT) cell. Commonly, the gas phase pressure decay is modelled by use of Fick's second law along with gas‐phase mass balance equations and assuming a constant diffusion coefficient. In this work, we evaluate two concentration‐dependent diffusion coefficient functions, power‐law and exponential. A simple history matching technique is used to estimate the apparent diffusion coefficient (Do) and concentration dependency factor (ma) from pressure‐decay data. Extensive application of our method to experimental pressure‐decay tests shows that in addition to constant diffusion coefficients, both power‐law and exponential functions are capable of predicting the experimental data. This implies that other experimental techniques are required to extract the functionality of diffusion coefficients with gas concentrations in heavy oil.
Mexico's oil production has been declining for the last decade. Therefore, the country has established strategies to increase oil production including the acquisition of new technology to produce unconventional reservoirs as well as the implementation of new regulations to enhance recovery rates from mature fields and develop the shallow-water and deepwater areas. This paper presents a detailed analysis of Mexico's new hydrocarbons legislation with special focus on the contracting and bidding processes. This research also considers available data to identify the main technical challenges associated with the contractual areas which ultimately may be crucial in increasing oil production. Prospective production from main Mexican reservoirs was evaluated using a probabilistic method based on decline curve analysis (DCA) to forecast Mexico's oil production and its effect on North America oil production outlook. The results of the technical evaluation of the contractual areas along with the analysis of the new policies indicate optimistic scenarios for the development of projects and a potential increase in oil production. These projects will foster offset decline of oil production by attracting experienced companies capable of facing current technical challenges and increasing upstream investment. Furthermore, areas of opportunity in the new regulations were identified to make the project conditions more attractive for companies and government. This study is built upon the exhaustive analysis of the new legislation and characteristics of the contractual areas in the context of the current internal and external factors to forecast Mexico's oil production scenario.
Solubility and diffusivity of gases in heavy oil, respectively quantified by Henry's constant (H ij ) and diffusion coefficient (D), are essential properties for the design of recovery processes that require the injection of gas or vapour solvents into the reservoir. Data, obtained from various experimental procedures such as the pressure-decay technique (PDT), are used to estimate these two parameters. The PDT uses a Pressure/Volume/Temperature (PVT) cell where the gas phase pressure declines as gas diffuses into heavy oil following an early-time and a late-time regime. Current approaches to analyze data from the conventional PDT are either graphical techniques based on early-time data or full numerical simulation. Early time data, the period in which the diffusing gas has not reached the bottom of the PVT cell, do not provide enough information to simultaneously estimate diffusion coefficient and Henry's constant. Hence, existing graphical procedures are limited to diffusion coefficient estimation.In this paper, a novel and simple graphical technique is proposed to estimate the diffusion coefficient and Henry's constant using the late-time data from pressure-decay experiments. The proposed method is based on modeling of gas phase pressure decay using Fick's second law and gas phase mass balance equations. The Integral method is used to provide an approximate, but analytical solution to the set of equations. The resultant solution is used to develop a simple graphical method, i.e. inverse problem, in which both diffusion coefficient and Henry's constant are directly estimated. The estimated parameters through the proposed technique for methane/bitumen and carbon dioxide/bitumen experiments are in close agreement with the values reported in the literature.
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