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
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.
The increasing need for continuous reservoir monitoring is one of the primary concerns to the oil industry to improve the hydrocarbon recovery factor and production efficiency. Several monitoring scenarios with geophysical methods can be derived including surface and borehole-based methods and their combinations. One is a surface electric current dipole and a vertical electric borehole receiver which has the strongest coupling in detecting the water flood front changes and is easy to implement. The surface-to-borehole electromagnetic if combined with seismic can give excellent resolving capabilities. A modeling study was performed to generate several results based on the given model. This is to support feasibility studies as well as to determine survey acquisition parameters. A 3-layer model was used with a hydrocarbon reservoir in the second layer. The optimum transmitter offset was determined by the modeling result and the value was used for the rest of the experiment. The resistivity of the hydrocarbon reservoir was also varied to observe the received vertical electric field. A time lapse study is relevant for the reservoir monitoring. We built and simulated 3-D model to apply this technology to real reservoirs. In combinations with reservoir simulator results it predicts the outcome of potential surveys. The model is then translated to time lapse fluid changes in order to design the survey layout such that we can get a maximum response.
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.
Nuclear Magnetic Resonance (NMR) mud logging technology has been widely used in Chinese oilfields and successfully solved many critical problems such as low SNR from small cuttings, well site reservoir characterization, rapid formation evaluation, and long sample preparation time for conventional core measurement. This technology realizes the transformation of reservoir petrophysical analysis from laboratory to drilling site, and extends the analysis samples from conventional cores to small fresh cuttings, sidewall cores and formation fluids. The formation petrophysical properties of small cuttings measured by NMR mud logging system include total porosity, effective porosity, absolute permeability, probable minimum and maximum permeability, irreducible water (liquid) saturation Swirr free water (fluid) saturation, oil saturation, etc. When used in the laboratory, it can deliver the most standard NMR petrophysical parameters. In addition, mud logging NMR has many advantages such as small sample quantity, short analysis time, low cost, nondestructive, multiple parameters from a single sample, high accuracy, excellent repeatability, measurement and analysis while drilling. It is a low-cost alternative for log calibration and even a replacement when it is difficult to obtain NMR logs from a wireline tool.
With NMR mud logging we can effectively evaluate the formation petrophysical properties, reserve and capacity of interstitial liquid by rapidly and accurately analyzing petrophysical parameters, such as porosity, permeability, FFI, BVI, oil saturation, etc., from cuttings, core plugs and sidewall cores on the drilling site, and then provide valuable and critical information for onsite decision-making of drilling and well completion. In recent years, a few thousands of cuttings and core samples have been measured by the NMR mud logging system and excellent application results of this technology have been achieved in such aspects as petrophysics evaluation, pore structure evaluation, pore fluid features evaluation, testing layer determination, and geopressure evaluation. The technology has been incorporated in the mud logging industry in six Chinese oilfields.
Oil and gas reservoirs are the formation of interest in exploration and production (E&P) activities; its properties controls hydrocarbon reserves, output and production capacities (Fang et al., 2003). Reservoir evaluation is very important in the course of E&P. With the rapid development of E&P technologies and the improvements of drilling techniques, the drilling rate is getting faster. At the same time, drilling cost (especially offshore) is increasing. Therefore, we must improve the reliability and authenticity of well evaluation results, as well as turn-around time.
Often, reservoir evaluation data comes from core analysis done in the laboratory or from well log interpretation. Limited by the availability of cores, the data volume of conventional core analysis is very small, and the analysis turn-around is slow. Especially, clay bound water and capillary bound water of core samples could not be measured by conventional core analysis techniques (Wang et al., 2005). Well logging is only conducted after the well has been drilled and completed, the timelines and accuracy cannot meet the demands of E&P. Although some models have been developed to quantitative evaluate the reservoir formation at the well site, one model is only for one parameter such as porosity or permeability.