Soultz-sous-Forêts Geothermal Reservoir: Structural Model Update and Thermo-Hydraulic Numerical Simulations Based on Three Years of Operation Data

The geothermal powerplant of Soultz-sous-Forêts (France) is investigating the possibility of producing more energy with the same infrastructure by reinjecting the geothermal fluid at lower temperatures. Indeed, during the operation of the powerplant, the geothermal fluid is currently reinjected at 60–70 °C in a deep fractured granite reservoir, and the MEET project aims to test its reinjection at 40 °C. A 3D hydrothermal study was performed in order to evaluate the spreading of the thermal front during colder reinjection and its impact on the production temperature. In the first step, a 3D structural model at fault scale was created, integrating pre-existing models from 2D vintage seismic profiles, vertical seismic profiles, seismic cloud structure and borehole image logs calibrated with well data. This geometrical model was then adapted to be able to run hydrothermal simulation. In the third step, a 3D hydrothermal model was built based on the structural model. After calibration, the effect of colder reinjection on the production temperature was calculated. The results show that a decrease of 10 °C in the injection temperature leads to a drop in the production temperature of 2 °C after 2 years, reaching 3 °C after 25 years of operation. Lastly, the accuracy of the structural model on which the simulations are based is discussed and an update of the structural model is proposed in order to better reproduce the observations.

Using Zero-Offset VSP to Identify Interbed Multiples Generators, A Case Study from South Oman

The presence of interbed multiples is a serious concern in surface seismic processing and interpretation. Its impact is huge especially if they are masking the desirable primary reflections such as the targeted reservoirs area. The conventional demultiple methodologies such as stacking, and deconvolution often fail to suppress all the interbed multiples. Therefore, a need for other measurement is crucial to eliminate the remaining ones (Burton and Lines, 1997). There are several approaches, data-driven or model-driven, currently available to predict the interbed multiples. However, they require an accurate identification of the multiple generators (Lesnikov and Owus, 2011). The identification of the origin of these multiples seems to be the most effective solutions to remove them, however it is not an easy task. The allure of Zero Offset Vertical Seismic Profiles (ZOVSPs) in having the receivers placed close to the subsurface horizons, allow both upgoing and downgoing wavefields to be recordable and separable. It's the combination of short window and long window deconvolution operators which are derived based on our knowledge of downgoing wavefield which help us to determine the multiples generators at their exact depths in the subsurface. This paper demonstrates how Zero offset VSP successfully helped to identify the major multiples generators in one of the exploratory fields in south Oman. These generators then used as an input to demultiple technique named as Extended Interbed Multiple Prediction (XIMP) that eliminates the multiples within surface seismic. As the result of the multiple elimination, the seismic to well tie tremendously improved and the reliability of the overall horizon interpretation is enhanced.

Frequent 4D monitoring with DAS 3D VSP in deep water to reveal injected water-sweep dynamics

Time-lapse monitoring using 3D distributed acoustic sensing vertical seismic profiles (DAS VSPs) is rapidly maturing as a nonintrusive low-cost solution for target-oriented monitoring in deep water. In a Gulf of Mexico field, DAS fibers deployed in active wells enable detailed tracking of the water flood in two deep reservoirs. Multiple tests in adverse well conditions let us understand the impact of source size and other factors on the spatially dependent quality of time-lapse DAS data and prove that excellent image repeatability is achievable under typical field conditions. Frequent repeat surveys allowed us to predict the timing of water arrival in a producer and to observe new water injection patterns that are important for understanding water-flood performance. Going forward, DAS 4D monitoring is envisioned as a tool that can assist with proactive wells and reservoir management, new well planning, and reservoir model updates.

Introduction to this special section: Reservoir monitoring

The papers submitted to this special section demonstrate that the topic of reservoir monitoring is extremely diverse. This diversity is reflected in the wide range of geologic settings covered by these papers — deepwater unconsolidated clastics, more cemented sandstones in onshore fields, and carbonates. Diversity is seen in the range of production scenarios described by these papers — water sweep of oil and gas, thermal recovery using steam-assisted gravity drainage (SAGD), and enhanced recovery using CO2 injection. Moreover, the papers in this section cover much more than time-lapse 3D seismic. Although about half of the submitted papers use 4D surface seismic data to monitor reservoirs, the remainder cover a diversity of methods that include time-lapse vertical seismic profiles (VSPs), repeat well logging using distributed acoustic sensing (DAS), and muon tomography. Even the concept of the “reservoir” is expanded to include monitoring microseismicity that might result from production activity.

Introduction to this special section: Borehole geophysics

When borehole geophysics technologies and applications come to mind, often we think of vertical seismic profiles (VSPs), checkshots, or wireline logging measurements. Problems that have been addressed include resolution enhancement, coverage, illumination, and time-to-depth conversion, among others. The papers in this special section, however, extend these relatively well-known techniques to include salt proximity work, use of high-pressure and ultrahigh-pressure geophones in VSPs, distributed acoustic sensing (DAS), acoustic wellbore ranging, refinement of velocity models and image enhancement, and impacts on business value. Although all the papers could have been about, for example, DAS or vertical resolution improvements, this special section turned out to be broader in terms of the application of borehole geophysics. What drives the need for borehole geophysics in these applications? Is it the significance of business value? Is it scientific and engineering knowledge? Is it some combination thereof? The answers to those questions are not addressed directly, but each paper is unique and offers useful results and techniques across many disciplines. This special section is not extensive in terms of the number of papers, but those included are well worth reading.

Migration-based filtering: Applications to geophysical imaging data

Migration is used to collapse “diffractions,” i.e., to focus hyperbolic events that appear in the space-time of a seismic profile — into spots of finite area in the image space. These usually represent scattering objects. However, there are situations in which some of the energy can be focused by migration, and muted without significantly damaging the remaining echoes. Demigration or forward modeling then restores the remaining data, and the removed signals can be rebuilt by subtracting these restored data from the original records. This process can be classified as migration-based filtering. It is demonstrated by synthetic and field data that this filter can be used for suppressing unwanted coherent signals or separating/extracting wavefields of interest: (1) the suppression of ground roll in seismic shot gathers, (2) the suppression of axially guided arrivals in borehole radar profiles, (3) suppressing the direct arrivals to enhance Stoneley-wave reflections in full-waveform sonic logging data, and (4) separating up- and downgoing waves in vertical seismic profiles.