--> Impact of CSEM Methods in Risk and Volumetric Evaluation of Prospects and Discoveries in Deep Water Gulf of Mexico

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Impact of CSEM Methods in Risk and Volumetric Evaluation of Prospects and Discoveries in Deep Water Gulf of Mexico

Abstract

Abstract

PEMEX has developed an integrated exploration process that includes basin to prospect studies that allow a correct evaluation of hydrocarbons prospective resources. The process is based on the main technical challenges of the projects that PEMEX operates.

Particularly on the Holok gas province, a big challenge was to decide if the amplitude anomalies in Miocene sediments were due either to commercial gas accumulations or to the presence of fizz gas, both cases present in the area, uncertainty remained despite intensive quantitative seismic studies performed by PEMEX. The Holok gas province has remaining prospective resources ranging between 5.5 to 16.5 Tcf which have to be evaluated in a way that assures efficiency for the exploratory investment.

In order to face this challenge, PEMEX acquired more than 5,000 km2 of controlled source electromagnetics data (CSEM) on the Holok province during 2011 and 2012, results were integrated with the current knowledge of the area. The surveys included discoveries and new prospects. A careful process of calibration was made using state-of-the-art technology supported by leading technology service companies.

Two amplitude-supported Miocene objectives were evaluated on both volumetrics and risk. Once the data is acquired, the methodology for the use of CSEM has three main phases: 1) Estimation of an initial resistivity model from well logs and seismic interpretation, 2) 3D resistivity inversion and 3) Integration with seismic data and geological framework.

During the predrill stage, recoverable hydrocarbon volumes were adjusted as well as geological risk based on the results of the resistivity inversion. These adjustments were performed comparing distribution of resistivity response, (both vertical and horizontal) and seismic amplitude response. As a result, the volumetric uncertainty was reduced and the risk decreased in the areas where there was a correspondence between resistivity and seismic.

Furthermore, once the prospects were drilled, an extraordinary match between proven hydrocarbons and areal distribution of resistivity was observed.

Therefore, the complete portfolio of Miocene targets in the Holok gas province was reevaluated in order to have a more precise estimation of prospective resources for this play in the province. Finally, all the prospects in the area with Miocene targets must have a positive resistivity response in order to be considered for drilling.