A new methodology to determine the potential SAGD, "Steam Assisted Gravity Drainage", application for Venezuelan reservoirs, with °API gravity less than 20, is proposed as a first phase to select the most proper candidates. A systematic ranking of all the possible reservoir candidates using screening criteria supported by statistical methods is performed. Based on the evaluation of several analytical models a more representative analytical tool was generated to evaluate and predict the performance of SAGD process. Also, this analytical tool was used to define the critical parameters and the statistical analysis was used to estimate the relative influence of each one. Ranking method was based on a similarity approach. By defining a reference reservoir from published field tests and comparing statistical distances from it thirty-five candidates were pre-selected from a total of 1067 Venezuelan reservoirs. The best candidates should be evaluated with more details through numerical simulations. The resulting technical efficiency and economic balance will be taken as a decision criterion for a field application. This methodology will facilitate the decisions related to the application of SAGD process to increase the recovery factor in Venezuelan heavy oil reservoirs and upon its potential massive application.
Although heavy oil has been produced in the Morichal area of Venezuela for over twenty-five years, significant advances have recently been made to improve performance of the heavy oil wells. These advances include new techniques for injecting a diesel diluent at the bottom of the well and further optimization of artificial lift systems. These new techniques have resulted in a significant increase in production over a short period of time with minimal outlay of resources.
The production of oil wells on intermittent gas lift can be increased by properly selecting the optimum cycle time and injecting the correct amount of gas at the required injection pressure in each cycle. Due to the complexity of the process, some times the production engineer is forced to perform downhole pressure surveys to have a better understanding of the well performance and therefore, improve the quality of the trouble shooting outcome. This kind of procedure is specially important for choke control intermittent gas lift where a precise knowledge of the inflow and outflow behavior of the well is needed. In this paper, a detailed description of the correct procedure for performing and analyzing a downhole pressure survey is given. The survey procedure is a combination of static and dynamic downhole surveys which when properly done and analyzed, will provide the following information:optimum cycle time;productivity index;current fallback;real fluid gradient;static reservoir pressure and other reservoir properties. The mathematical procedure used to find the liquid slug length as a function of time and the productivity index is derived in the paper and a computer algorithm to perform these tasks is presented. Actual downhole measurements closely match the computer output. A 30% increase in production was obtained when the procedure presented in this paper was applied to 10 wells in Lake Maracaibo Gas Lift Field. The surveys outcome and the necessary adjustments are also presented in the paper. P. 205
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