A new microseismic-electromagnetic (EM) acquisition system for reservoir monitoring includes surface and borehole hardware, processing software and interpretation methodology. For heavy oil reservoirs it allows mapping of steam/water flood fronts and surveillance of cap-rock integrity. The new array acquisition architecture combines novel technologies which reduces operational cost, due to unlimited channels capability: EM and microseismic acquisition is in the same receiver node to optimize the synergy between the methods.
While microseismic channels address seal integrity information, EM data are used to track fluids, due to their high sensitivity to the fluid resistivity. The fluid resistivity drops strongly with mobility increase and pore size variation. Dense data further reduce the cost per receiver in a surface location. EM channels provide three-component (3C) electric and 3C magnetic data acquired on the surface and in shallow vertical boreholes. For later versions and deeper reservoirs deep wireline receiver with through casing measurement capabilities are planned. We include in the system an independent physics verification measurement using a differential approach to the surface data called focused source EM (FSEM) with practically little cost.
Carrying out feasibility for each reservoir is key to control risk and cost. The feasibility includes 3D EM modeling, which allows integrating typically complex nature of the reservoir, and on-site EM noise test to tie 3D modeling to actual measured voltages.
3D modeling feasibility for a heavy oil reservoir proves the methodology to monitor the boundaries of the steam flood with accuracy and with high fidelity. Above the edges of the flooded (higher-temperature – lower-resistivity) area the results predict time-lapse EM anomaly exceeding 500%.
The entire system is coupled with processing and 3D modeling/inversion software, significantly streamlining the workflow for the different methods.
The system is capable of measuring and integrating the 3C of the electric field and 3C of the magnetic field in order to map the steam front and at the same time measuring microseismic occurrences in order to monitor seal stability. Channels capability of the system is practically unlimited allowing a denser coverage of the area in order to increase resolution and improve inversion.
A new technology for reservoir monitoring includes full field controlled-source electromagnetics (CSEM) and microseismics. To mitigate the risk, we have developed full technology cycle: from patents, hardware, acquisition methodology, to data processing and interpreting in 3D. The system can acquire surface-to-surface and surface-to-borehole measurements. EM data are used to track fluids, due to their high sensitivity to the fluid resistivity while seismic data relate primarily to the reservoir boundaries. Having seismic and EM sensors in the same recording unit allows the addressing of the multi-physics character of the problem early on in the workflow. The system enables acquiring large number of EM data channels at low cost similar to what is done with seismic data.
Typical risks are lack of EM image focus, formation resistivity anisotropy and unaccounted effects of steel casing(s). To mitigate these risks, we apply careful 3D modeling feasibility studies and acquire dense EM field data. In addition, we apply a novel method to focus the EM image information directly below the receiver. Operational risks include low signal-to-noise (SNR) ratio, issues related to the transmitter stability, to the stability of the groundings, and data processing inefficiency. Understanding and mitigation of these risks is key to successful reservoir monitoring job.
Presentation Date: Tuesday, October 16, 2018
Start Time: 9:20:00 AM
Location: Poster Station 15
Presentation Type: Poster
Heavy oil (HO) is often produced with Enhanced Oil Recovery (EOR) methods such as steam or water flooding. In addition to flood front movements reservoir seal integrity has become an issue. Seal integrity is best addressed with microseismics and water flood front bets with electromagnetics. We address the fluid imaging problem using electromagnetics and after careful 3D feasibility and noise tests. We selected Controlled Source Electromagnetics (CSEM) in the time domain as the most sensitive method. From the 3D modeling we derived as key requirement that borehole and surface data needed to be integrated by measuring between surface to borehole and also calibrated using conventional logs.
Depending on the resistivity contrasts between the reservoir and the surrounding formation we need to measure electric AND magnetic fields as each of them have different sensitivity. The magnetic field senses more conductive strata, while the electric field will define fluid changes inside the HO reservoir. Furthermore, for shallow reservoir multi-frequency band sensors need to be deployed to get the optimum sensitivity.
Over the last decades we carried out 3D feasibilities for many oil fields and we are presently conducting the FIRST steam flood Pilot in an oil field in Asia. We also design custom data acquisition system for land, marine and borehole. Carrying out a Feasibility for each reservoir is key to control risk and cost. 3D modeling allows to integrate complex nature of the reservoir by constraining the model with existing seismic data. In all hydrocarbon cases it shows the need for full tensor CSEM, surface and borehole measurements to effectively determine the HO/steam flood front.
With the increasing success of marine electromagnetics, the trend is to go to similar acquisition density as with seismic data. Cabled marine controlled source electromagnetic (CSEM) systems under development will make acquisition of dense CSEM datasets for seafloor exploration practical. Natural source EM data, which may also be collected by such systems for essentially no additional cost, have the potential to refine and confine the interpretation of the CSEM data in complex and variable geologic environments. However, to reduce costs and maintain operational efficiency in a cabled system only some components of the EM fields may be collected, so that the configuration of sampled data may be non-standard for classical magnetotellurics. Specifically, spacings will be closer but not all components are measured at every site. Here we use 3D synthetic data inversion experiments to explore impacts on target recovery of (1) sampling density, and (2) exclusion of specific transfer function components. We show that including magnetic field TFs almost completely compensates for exclusion of impedance components associated with cross-profile electric fields, which would be more challenging to collect with a cabled system.
2-D AMT/MT and gravity surveys were completed in 12 su survey areas in Hungary during 2008. The main objective of this project was to locate potential geothermal targets for alternative energy development in Hungary. We selected here the Szentlo¨rinc (Szl) survey area because the geothermal drilling project just completed. The main geothermal reservoir systems found in Hungary are the Mesozoic carbonate-karstic basement rocks and the Pliocene-Upper Pannonian porous sedimentary formations (A´rpa´si, Lorberer, and Pap, 2000). The interpretation of 2-D AMT/MT and gravity focuses on locating potential geothermal areas of the geothermal reservoir system within Mesozoic fractured carbonate-karstic basement rock for drilling locations. We estimated that the faults within the north-south strike in the Szl survey area were developed in the deep basement. In addition, dense fractures have also been widely developed in the top basement (limestone) of the two survey areas. Thermal energy, which was transported up along the fault systems from the deep Earth, seems to be the heat source of geothermal formation. A set of thick tertiary deposits, are located above the formation. Fractured karst limestone and dolomite deeply buried in the Mesozoic system contain the targeted geothermal reservoirs. Based on the cooperative constrained inversion of magnetotelluric (MT) and gravity data, we surmise that the geothermal aquifer is characterized by a relatively low apparent resistivity and low density, while the higher porosity and permeability formations are unique for faults and fractured zones. The distribution characteristics of the fault zones with relatively low resistivity and with boundaries outlined by cooperative constrained inversion of MT and gravity data indicate that the prospective zones for potential geothermal reservoirs in the Szl survey area indicate that the mid-northern part of AMT/MT line 1 and the middle part of AMT/MT line 2 are potential areas for geothermal power plants or space heating.
Yu, Gang (KMS Technologies) | Strack, Kurt (KMS Technologies) | Allegar, Norman (KMS Technologies) | Gunnarsson, A´rni (Landsvirkjun) | He, Zhanxiang (BGP) | He, Lanfang (BGP) | Tulinius, Helga (VGK-Ho¨nnun)
He, Lanfang (BGP) | He, Zhanxiang (BGP) | Strack, Kurt (KMS Technologies) | Allegar, Norman (KMS Technologies) | Yu, Gang (KMS Technologies) | Tulinius, Helga (VGK) | Ádám, László (VGK) | Halldórsdóttir, Heiða (VGK)
Recent advances in electronics now enable time-domain, or transient CSEM data, to be reliably acquired in an offshore environment and make the leap from its dominant position in land EM to the marine world. Multiple surveys using autonomous receiver nodes have successfully acquired marine time domain CSEM data. The approach has shown particular benefit in shallow water since the method records only the secondary fields and the signal is not dominated by the primary field.