Regional Drawdown Research Articles

Integrating 4D Data Into Dynamic Model Improves Johan Sverdrup Field Development

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209541, “Integration of Johan Sverdrup PRM 4D Data Into the Dynamic Model,” by Monica A. Calvert, Yuri Tsaplin, and Hans P. Hansen, TotalEnergies. The paper has not been peer reviewed. _ The Johan Sverdrup field permanent reservoir monitoring (PRM) system now has recorded two surveys documenting the progression of the waterflood since production and injection began in October 2019, revealing a clear 4D signal linked to the increase in water saturation. The 4D signals have been used to help guide updates within the reservoir model, providing a better understanding of how the field development is progressing. Field Background and PRM System The giant Johan Sverdrup oil field was discovered in 2010 in the North Sea approximately 150 km west of Stavanger. The field is laterally extensive, covering 200 km2 and consisting primarily of Upper Jurassic intra-Draupne sandstone and Upper Triassic-Lower Jurassic Statfjord sandstones in a low relief structure. The reservoir is characterized by excellent porosity and permeability, with drillstem tests showing permeabilities of up to 70 darcies with good communication over long distances and across faults. The oil is undersaturated with a low gas/oil ratio and is normally pressured, with slight depletion from a regional drawdown. Reservoir thickness varies across the field, with the intra-Draupne sandstone ranging from 5 to 40 m. The primary drainage strategy includes initial waterflooding to be supplemented by water-alternating-gas injection at the end of the oil-production plateau. The full field development consists of 64 wells, both platform and subsea. Producers are placed on the structural highs with water injectors placed on the flanks below the initial oil/water contact (OWC). Because of full voidage replacement by water injection, reservoir pressure is expected to stay fairly constant during field life. Johan Sverdrup is the first oil field to have a PRM system installed before production startup. The PRM system is a key component of the reservoir-monitoring and data-acquisition plan and was installed in two stages in 2019 and 2020 (Fig. 1). Yearly monitor surveys are planned to monitor waterflood development. The first seismic acquisition in 2019, referred to as PRM0, covered the initial first stage of installation on the northern part of the field. Stage two of the installation was completed in 2020, and two monitor surveys have since been acquired, covering the entire field, in 2020 (PRM1) and 2021 (PRM2). Feasibility studies show that a 4D response would be detectable within the reservoir. The increase in water saturation caused by water injection and upward movement of the OWC yields an increase in acoustic impedance, or hardening, in the reservoir. For the 4D analysis, the main seismic surfaces used were the Top Aasgard formation, the Top Viking group (which contains the Draupne formation), and the Intra Upper Triassic Unconformity (IUTU). The acoustic impedance increase measured in the 4D seismic data is compared with water-saturation changes within the reservoir model. Differences between the two can highlight areas within the reservoir model that require updating.

Modeling a Large-Scale Historic Aquifer Test: Insight into the Hydrogeology of a Regional Fault Zone.

Faults can act as flow barriers or conduits to groundwater flow by introducing heterogeneity in permeability. We examine the hydrogeology of the Sandwich Fault Zone, a 137 km long zone of high-angle faults in northern Illinois, using a large-scale historic aquifer test. The fault zone is poorly understood at depth due to the majority of the faults being buried by glacial deposits and its near-vertical orientation which limits geologic sampling across faults. The aquifer test-perhaps one of the largest in terms of overall withdrawal in North American history-was conducted in 1942 at a facility adjacent to the fault zone. More than 34,000 m3 /day was pumped for 37 days from nine multiaquifer wells open to the stratified Cambrian-Ordovician sandstone aquifer system. We modeled the aquifer test using a transient MODFLOW-USG model and simulated pumping wells with the CLN package. We tested numerous fault core/damage zone conceptualizations and calibrated to drawdown values recorded at production and observation wells. Our analysis indicates that the fault zone is a low-permeability feature that inhibits lateral movement of groundwater and that there is at least an order of magnitude decrease in horizontal hydraulic conductivity in the fault core compared to the undeformed sandstone. Large head declines have occurred north of the fault zone (over 300 m since predevelopment conditions) and modifying fault zone parameters significantly affects calibration to regional drawdown on a decadal scale. The flow-barrier behavior of the fault zone has important implications for future groundwater availability in this highly stressed region.

Mitigating depletion of a porous geothermal aquifer in the Pannonian sedimentary basin

This paper investigates depletion rates and available thermal water resources of the transboundary Upper Pannonian loose sandstone geothermal aquifer of the Mura Formation in the Mura-Zala sedimentary basin in north-eastern Slovenia, and outlines a regional reinjection strategy to mitigate depletion. The research monitoring network of 12 geothermal wells, which is being constantly upgraded since 2009, has highlighted that the current abstraction rate of 2.4 million m3 in 2014 is not sustainable because hydraulic state has been continuously deteriorating regionally while the chemical state is affected only locally. The average regional drawdown rate in observation wells is 0.67 m annually, while very rough average value for abstraction wells is 3.0 m per year. The cumulative historical regional drawdown is above 16 m. The available thermal water resources are addressed as the cumulative abstraction rate which reverses the observed declining trend of groundwater levels, and were numerically assessed to be ~1.3 million m3 of thermal water per year. These numerical models set up in the AUTOUGH2 code also provided the quantification tool of the regional groundwater balance and confirmed the gravity-driven regional groundwater flow with prevailing conductive heat transfer mechanism. Simulations of the regional reinjection strategy outline that the cumulative reinjection rate of ~1.48 million m3 of thermal water per year should be sufficient to reach good status of the aquifer if the cumulative regional abstraction rate does not change. If it does, the rate should be adjusted accordingly. The water is provided by eight users of geothermal heat and should be returned by the existing reinjection wells in Lendava and Murska Sobota and two new wells situated in the central part of the basin by 2021 the latest. These findings should enhance optimization of exploitation practice and implementation of geothermal doublets in the region as the successful example of a doublet in Lendava exemplifies that no major technological issues should occur if the system is properly designed.

Incorporating the effect of gas in modelling the impact of CBM extraction on regional groundwater systems

Production of Coalbed Methane (CBM) requires extraction of large quantities of groundwater. To date, standard groundwater flow simulators have mostly been used to assess the impact of this extraction on regional groundwater systems. Recent research has demonstrated that predictions of regional impact assessment made by such models may be seriously compromised unless account is taken of the presence of a gas phase near extraction wells. At the same time, CBM impact assessment must accommodate the traditional requirements of regional groundwater modelling. These include representation of surficial groundwater processes and up-scaled rock properties as well as the need for calibration and predictive uncertainty quantification. The study documented herein (1) quantifies errors in regional drawdown predictions incurred through neglect of the presence of a gas phase near CBM extraction centres, and (2) evaluates the extent to which these errors can be mitigated by simulating near-well desaturation using a modified Richards equation formulation within a standard groundwater flow simulator. Two synthetic examples are provided to quantify the impact of the gas phase and verify the proposed modelling approach (implemented in MODFLOW-USG) against rigorous multiphase flow simulations (undertaken using ECLIPSE∗). ECLIPSE simulations demonstrate convergence towards a time-asymptotic relationship between water saturation and pressure. This relationship can be approximated using a slightly modified van Genuchten function. Where this function is employed in combination with the modified Richards equation strategy to accommodate near-well desaturation, errors in predicted drawdown are reduced significantly, including in cases where complexities such as sloping coal layers are introduced to the model domain (the latter promoting buoyancy-driven movement of gas). Sensitivity analyses further indicate that only the general properties of the employed desaturation function need to be respected to significantly reduce errors in regional drawdown predictions that would arise if the presence of the near-well gas phase was ignored. These properties can be inferred from reservoir properties and from the outcomes of reservoir model simulations that are available at local CBM operation sites.

Integrating hydrodynamic analysis of flow systems and induced-pressure decline at the Otway CO2 storage site to improve reservoir history matching

The CO2CRC Otway Project is the first demonstration scale project for geosequestration of CO2 in Australia. The storage site is located in the depleted Waarre reservoir of the Naylor gas field contained within a single fault block, in the onshore Otway Basin of Victoria. During 2009, approximately 65,000 tonnes of a mixture of CO2 and CH4 (∼80%/20%) was injected into the reservoir, accumulating at the top of the structure.To fully understand the pressure response of a depleted reservoir to CO2 injection all of the mechanisms that may impact the reservoir pressure, prior to injection, must be identified. In the case of the Otway Project there were five possible mechanisms with potential for impacting the Naylor Field pressure. These are (1) the rate of recovery due to gas production from the Naylor Field; (2) depletion from the nearby Boggy Creek CO2 production field; (3) depletion from the nearby Buttress CO2 Field, the source of the CO2 for injection into the Naylor Field; (4) depletion from the regional Waarre Formation reservoir which has been producing gas (and water) since 1986; and (5) hydraulic potentiometric disequilibrium via connection to other active aquifers.These mechanisms were examined through a regional conceptual hydrodynamic model as part of the pre-injection site characterisation. The reservoir pressure measured at the Naylor-1 well, prior to production, was lower than predicted by the hydrodynamic model. Examination of regional drawdown demonstrated that the reservoir is experiencing pressure decline which could have extended to the Naylor Field at this time.Ongoing monitoring of the Naylor-1 well, prior to injection, showed the depleted reservoir recovering faster than predicted by the reservoir simulation model matched to the production history. Connecting the target fault block to the regional aquifer using a dual aquifer model supported by the hydrodynamic model significantly improved the predicted recovery of the depleted reservoir.

Changing Climate and Sea Level Alter Hg Mobility at Lake Tulane, Florida, U.S.

Between 45,000 cal years BP and the beginning of the Holocene, the accumulation rate for Hg in sediments of Lake Tulane, Florida ranged from ≈2 to 10 μg m(-2) yr(-1), compared with 53 μg Hg m(-2) yr(-1) in the 1985-1990 period of anthropogenic input. The locality experienced regional draw-down of the water table during the Wisconsinan glaciation, which lowered global sea level by nearly 130 m. Natural atmospheric deposition of Hg to the surrounding area resulted in long-term (ca. 100,000 years) sequestration of this atmospheric flux of Hg, primarily by adsorption in the oxic Al- and Fe-hydroxide-rich sandy subsoil. Global sea level rise during deglaciation led to a rising regional water table, flooding the oxidized soils surrounding Tulane. Iron and adsorbed Hg were mobilized by reductive dissolution and transported by groundwater flow to Lake Tulane and ultimately to the accumulating sediment. The accumulation rate of Hg (and Fe) increased rapidly about 16,000 cal years BP, peaked at nearly 60 μg Hg m(-2) yr(-1) ca. 13,000-14,000 cal years BP, declined sharply during the Younger Dryas, and then increased sharply to a second 60 μg Hg m(-2) yr(-1) peak about 5000 cal years BP. Thereafter, it declined nearly to background by 900 cal years BP. In similar geologic situations, rapid modern sea level rise will initiate this process globally, and may mobilize large accumulations of Hg and lesser amounts of As, and other redox sensitive metals to groundwater and surface water.

Influence of rapid glacial retreat on the rate of erosion by tidewater glaciers

Research Article| January 01, 2002 Influence of rapid glacial retreat on the rate of erosion by tidewater glaciers Michèle N. Koppes; Michèle N. Koppes 1Quaternary Research Center, Box 351360, University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Bernard Hallet Bernard Hallet 1Quaternary Research Center, Box 351360, University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Geology (2002) 30 (1): 47–50. https://doi.org/10.1130/0091-7613(2002)030<0047:IORGRO>2.0.CO;2 Article history received: 24 Apr 2001 rev-recd: 29 Aug 2001 accepted: 26 Sep 2001 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Michèle N. Koppes, Bernard Hallet; Influence of rapid glacial retreat on the rate of erosion by tidewater glaciers. Geology 2002;; 30 (1): 47–50. doi: https://doi.org/10.1130/0091-7613(2002)030<0047:IORGRO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Glacial erosion rates inferred from total sediment budgets in recently deglaciated fjords, which are the highest reported erosion rates worldwide, have received considerable attention in fields as diverse as tectonics, glacial sedimentation, and climate. These record rates, however, are representative only of tidewater glaciers during their extensive retreat of the post–Little Ice Age period; erosion rates averaged over glacial-interglacial cycles and longer periods are likely to be substantially smaller. We examine the influence of retreat rate on sediment yields from tidewater glaciers by reconstructing the history of sediment output from retreating glaciers necessary to produce sediment packages observed in contemporary fjords. Using a simple numerical model of proglacial sedimentation in front of a retreating glacier, seismic profiles of proglacial sediments, and the history of terminus retreat of Muir Glacier, Glacier Bay, Alaska, we calculate the sediment flux as a function of time from this glacier between 1900 and 1979, and conclude that sediment flux scales with retreat rate. The corresponding basin-wide erosion rate during this 79 yr period averages 37 mm/yr, and exceeds long-term erosion rates by a factor of 5 ± 1. For Muir Glacier and, by inference, for other calving glaciers, the general drastic retreat and the marked regional drawdown of ice since the Little Ice Age are both linked to unusually rapid calving and fast ice motion, which is conducive to rapid erosion. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Discussion on ‘The use of a numerical model in the management of the Chalk aquifer in the Upper Thames Basin’ by E. H. Morel

M. Owen writes: The area studied by the author is the location of the existing Stage 1 and proposed Stage 2 of the Thames Groundwater Scheme for augmenting river flow at times of severe drought. For an aquifer model to produce reliable forecasts of various management options for developing groundwater resources it must represent real conditions as closely as possible. This requirement is particularly difficult to achieve in an aquifer such as the Chalk which, except in conditions of restricted space and time, must be regarded as heterogeneous. The characteristics of the aquifer in the study area are well demonstrated by field evidence which should be the basis of the model. The representation of this evidence in the model is covered in the following discussion of this paper by Connorton. In assessing the yield of a major groundwater resource development in relation to the aquifer and not the engineering works, the following criteria should be considered: Resources—natural and artificial recharge and volume in storage. Storage removal—regional drawdown in relation to effective saturated depth. Net gain—the proportion of pumped water which is added to supply. Connorton later explains how Morel's basic approach to modelling produces unrepresentative distributions of transmissivity and storativity in relation to the operational conditions of the scheme. The over-optimistic predictions that are likely to arise from Morel's model apply particularly to the estimates of the volume in storage and regional drawdown, and therefore lead, under criteria (i) and (ii), to misleadingly high estimates of the quantity