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Alcocer, José Antonio Escalera (PEMEX Subdirección de Exploración) | Soto, Humberto Salazar (PEMEX Subdirección de Exploración) | García, Marco Vázquez (PEMEX Subdirección de Exploración) | Roth, Friedrich (EMGS) | Baltar, Daniel (EMGS) | Gabrielsen, Pål T. (EMGS) | Paramo, Valente Ricoy (EMGS)
In this paper we describe the highlights from a wide range of CSEM applications and developments in the Wisting area. At an initial stage, by including higher frequencies in 3D CSEM inversion at Wisting, we realized that our CSEM data contained a lot more detailed information about reservoir properties than earlier anticipated. Beyond the traditional application of predicting high vs. low hydrocarbon saturation, the CSEM data are used for estimation of reservoir heterogeneity and even connectivity. Our quantitative workflows are still maturing and are expected to provide future value. At Wisting we have been fortunate to be in an active appraisal setting where new wells have repeatedly provided calibration and adjustment to our CSEM workflows. During almost four years we have acquired two field-scale tailored 3D CSEM surveys with gradually denser spatial sampling and higher frequencies. These have provided higher accuracy and better spatial resolution than the conventional coarse-grid survey design used in multi-client projects. Our project work has been highly cross-disciplinary, where CSEM expertise paired with specialists in rock physics, seismic AVO and geology has worked very well. Our ability to operate as one team across company barriers is a key success factor with learning, re-learning and geoscience integration as main ingredients.
Presentation Date: Thursday, September 28, 2017
Start Time: 8:30 AM
Presentation Type: ORAL
While seismic has a superior structural resolution and is sensitive to porosity and the presence of hydrocarbons, it has very little sensitivity to saturation. Controlled-source electromagnetic (CSEM) is, on the other hand, sensitive to hydrocarbon saturation. Thus, joint interpretation of seismic and CSEM inversion results offer a great potential for hydrocarbon saturation and volume estimations. We describe a new workflow employing high resolution deterministic CSEM inversion and statistical seismic AVO inversion that applies in an exploration setting, i.e. without prior assumptions of the background resistivities or the existence, sizes and shapes of resistive anomalies. The high resolution deterministic CSEM inversion has proven better depth placements and more confined resistive anomalies by incorporating seismic horizons into the inversion. We use a statistical AVO inversion for lithology and fluid predictions, called PCube, where a prior model for the elastic properties is defined for different lithology and fluid classes (LFCs) based on geological knowledge and/or information from nearby wells. PCube outputs posterior probability for each LFC specified in the prior model. The inversion results from CSEM and seismic are then co-interpreted utilizing their complementary information. This offers a direct comparison between expected hydrocarbon-filled reservoirs from seismic and whether these reservoirs are of high or low saturation from CSEM inversion results, and to explain resistive anomalies not related to hydrocarbons. Applying the workflow on Skrugard datasets, the joint interpretation clearly shows the ability to discriminate high hydrocarbon saturated from brine/low saturated sand reservoirs. Furthermore, the workflow can also distinguish hydrocarbon related from non-hydrocarbon related resistive anomalies.
Abstract The Ganges Brahmaputra Delta and the associated Bengal Fan is the world's largest delta/submarine fan complex. The deepwater areas of the Bengal and Rakhine Basins are relatively underexplored frontier areas. In 2003 the large Shwe gas field was discovered in Lower Pliocene turbidite fan sediments with reserve estimates of 6–9 tcf. As additional blocks are licensed, new data will be acquired to evaluate the area including 3D CSEM which is being considered as a complementary exploration method to seismic data. The controlled-source electromagnetic (CSEM) method has been applied to oil and gas exploration and production for more than 10 years. EM data are used to indicate the presence of hydrocarbons, since hydrocarbon saturated rocks display higher electric resistivity compared to water-filled reservoirs. CSEM is an excellent technique to define the lateral extent of hydrocarbon accumulations and is particularly useful in determining the existence and extent of stratigraphic accumulations. 3D modelling indicates CSEM is sensitive to the Shwe Field reservoirs and can define the lateral extent of the pay zones. 3D CSEM forward modelling has been performed over a range of target sizes within the economic limitations of deepwater drilling, and the modelling shows that CSEM would be sensitive to those targets. Based on these results, it is concluded that CSEM 3D data will detect the presence of hydrocarbon accumulations and thus, high-grade exploration areas in the greater Bengal Basin. Introduction In this paper we describe how the deepwater reservoir sediments in the Bay of Bengal, dominated by a deepwater turbidite depositional process, is the ideal geologic setting for detecting resistive anomalies related to hydrocarbon accumulations. Turbidites, by nature, are anomalous deposits of sand encased in shale. When saturated with hydrocarbons, they are more resistive than the surrounding shales, allowing them to be detected using the marine controlled source electromagnetic (CSEM) method. CSEM is sensitive to the large Shwe field accumulation on the shelf, offshore Myanmar and is used in this study to illustrate the ranges of detectability in the adjacent deepwater areas (Fig. 1).
Nguyen, Anh Kiet (Statoil ASA) | Nordskag, Janniche Iren (Statoil ASA) | Wiik, Torgeir (Statoil ASA) | Bjørke, Astrid Kornberg (EMGS ASA) | Boman, Linus (EMGS ASA) | Pedersen, Ole Martin (EMGS ASA) | Ribaudo, Joseph (EMGS ASA) | Mittet, Rune (EMGS ASA)
Electromagnetic signals are exponentially attenuated in However, due to the strong exponential attenuation of the conductive media. Thus, marine controlled-source EM signal, a small error in the model used to estimate the electromagnetic (CSEM) data where the source and the sensitivity causes large errors in the sensitivity receivers are located in the water column has exponentially compensation, leading to poor inversion results. More low sensitivity towards the deep stratigraphy, compared to advanced gradient based methods, like BFGS, where the the shallow stratigraphy. In addition, CSEM inversions are Hessian is estimated from the gradients of a limited number also highly nonlinear and ill-posed. It is therefore often of previous iterations, may improve the inversion results.