Steineder, Dominik (OMV Exploration and Production) | Clemens, Torsten (OMV Exploration and Production) | Osivandi, Keyvan (OMV Exploration and Production) | Thiele, Marco R. (Streamsim Technology and Stanford University)
Polymer injection might lead to incremental oil recovery and increase the value of an asset. Several steps must be taken to mature a polymer-injection project. The field needs to be screened for applicability of polymer injection, laboratory experiments have to be performed, and a pilot project might be required before field implementation.
The decision to perform a pilot project can be dependent on a value-of-information (VOI) calculation. The VOI can be derived by performing a work flow that captures the effects of the range of geological scenarios, as well as dynamic and polymer parameters, on incremental net present value (NPV). The result of the work flow is a cumulative distribution function (CDF) of NPV linked to prior distributions of model parameters and potential observables from the polymer-injection pilot.
The effect of various parameters on the CDF of the fieldwide NPV can be analyzed and in turn used to decide which measurements from the pilot have a strong sensitivity on the NPV CDF, and are thus informative. In the case shown here, the water-cut reduction in the pilot area has a strong effect on the NPV CDF of the polymer-injection field implementation. To extract maximum information, the response of the pilot for water-cut reduction needs to be optimized under uncertainty.
To calculate the VOI, the expected-monetary-value (EMV) difference of a decision tree with and without the pilot can be used if the decision maker (DM) is risk neutral. However, if the DM requires hurdle values through a probability of economic success (PES), value functions (VFs) and decision weights according to the prospect theory should be used. Applying risk hurdles requires a consistent use of VFs and decision weights for calculating VOI and the probability of maturation (POM) of projects.
The methodology was applied to assess the VOI for a horizontal-well pilot in the ninth Tortonian Horizon (9TH) Reservoir in Austria for a risk-averse DM. The operating parameters (polymer concentration and water injection) were chosen such that the watercut reduction, which was the most influential parameter of the polymer pilot on the field NPV CDF, was maximized.
The paper covers the construction and use of large caverns for temporary and permanent purposes on the example of the 27km long Semmering Base Tunnel in Austria. Semmering Base Tunnel is a twin tube, single-track railway tunnel with numerous cross passages and an underground emergency station with ventilation located approximately at the center of the tunnel system. The construction started in 2014 and is ongoing until 2026.
The emergency station, which is located at the toe of two 400 m deep shafts, requires the construction of large permanent caverns with dimensions in the range of 20 by 18 m. The available space in these caverns will also be used during construction for the placement of site installations underground in order to optimize the logistic procedures and avoid disruptions in supply and discharge via the shafts.
Intermediate access points are provided by 120 to 200 m deep shafts, which also require the construction of temporary caverns at the shaft bottom for site installations, material storage and transport purposes. In one case even shaft head caverns are carried out as the shafts start underground at the end of a 1.2 km long access tunnel.
For the construction in difficult geological conditions complex headings and special support measures using the SEM are applied. Advanced numerical 2D- and 3D-calculations were carried out to verify the adequacy of the designed solutions. The final configuration of the permanent and temporary caverns includes the installation of a drained, secondary lining or a complete backfill in case of the temporary structures.
The content of the paper covers the construction of temporary and permanent caverns at the example of an actual project currently carried out in Austria.
The boundary conditions requesting the construction of the caverns such as safety regulations, logistic purposes or overall schedule requirements are addressed.
The chosen solutions for the construction of the caverns as well as its configuration for the temporary and the final stage are presented.
2. Project overview
Semmering Base Tunnel is located app. 80 km south of Vienna in Austria and is part of the Baltic-Adriatic Railway Corridor, which runs between the Baltic Sea from Gdansk in Poland to the Adriatic Coast near Bologna in Italy (see Figure 1).
The PDF file of this paper is in Russian.
Polymer Flooding has been shown to increase oil production. The reason for increasing oil production is acceleration along flow paths but also flow diversion from higher permeability to lower permeability areas. Tracer tests performed in the 8 TH Reservoir in Austria prior, during and after polymer flooding show that the flow system dramatically changed. The connected volumes from injector to producer as well as the flow heterogeneity were influenced and substantial incremental oil produced. A number of tracer tests were performed in the pilot area of a polymer flood at various times. In addition, pressure data and polymer rheology was analyzed.
The tracer results were used to calculate flow pattern, dynamic Lorentz coefficient and connected volumes. Pressure data were used in combination with geomechanical modelling to investigate the injection regime (matrix or fractures). The interpretation of the data was combined with the determination of incremental oil production based on simulation. The tracer tests reveal the dramatic changes in flow patterns, connected volume changes by more than a factor of three occurred and the Lorentz coefficient indicating the heterogeneity of flow changed by more than a factor of two. The injection regime changed from injection under matrix conditions prior to polymer flooding to injection under fracturing conditions during polymer injection and back to injection in matrix conditions during chase water injection.
The reason for the changes in injection conditions is the near-wellbore viscoelastic rheology of the High Molecular Weight Polymers which were used. The growth of fractures leads to additional alteration of flow paths. The design of polymer flooding needs to take into account that flow paths are not only changed due to the reduction in water relative permeability resulting from polymer adsorbing to the rock and the increased viscosity of the injected fluid but also owing to changes in injection regime. The changes in injection regime might lead to early breakthrough of chase water as it might not flow along the same paths as the polymer solution.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 180181, “Catalog of Well-Test Responses in a Fluvial Reservoir System,” by J.L. Walsh and A.C. Gringarten, Imperial College London, prepared for the 2016 SPE Europec featured at the 78th EAGE Conference and Exhibition, Vienna, Austria, 30 May–2 June. The paper has not been peer reviewed.
Well-test analysis in fluvial reservoirs remains a challenge because of the depositional environment conducive to significant internal heterogeneity. Analytical models used in conventional analysis are limited to simplified channel geometries and, therefore, fail to capture key parameters such as sand-body dimensions, orientations, and connectivity, which can affect control-fluid flow and pressure behavior. The complete paper aims at a better understanding of the effect of channel content in complex fluvial channel systems on well-test-derivative responses.
Geological Modeling. 3D geological models with a centrally located well were generated and populated with varying fluvial geologies. A 6950-m×6950-m×300-ft geological model was set up that allowed the averaging effects of the heterogeneities and the reservoir boundaries to be visible on the derivative at late times.
Modeling the geology of a fluvial system is challenging because of changes in channel amplitude, amalgamation, and other processes through geological times, which yield highly variable distribution and shapes of fluvial deposits. Field X was modeled as isolated elliptical sand bodies and channel bodies, with sand-body dimensions of 105 m (width)×420 m (length)×5 ft (thickness) for the base case. The sand and channel bodies are schematically represented in Figs. 1 and 2. Object-oriented modeling was used instead of stochastic, sequential indicator simulation and Gaussian simulation to retain control over the modeling parameters.
Numerical Simulation. The corresponding pressure and derivative dynamic responses were generated using a proprietary finite-element simulator with a uniform grid and a fine local grid refinement (LGR) around the wellbore. The fluid was black oil at a reservoir pressure greater than the saturation pressure, and the relative permeability to water was low enough to limit water movement within the model.
Results and Discussion of Base-Case Model
A drawdown of 115 years was simulated for a geological model 6950 m×6950 m×300 ft with a cell size of 50 m×50 m×5 ft in the x, y, and z directions, respectively (total cell count without LGR=1,159,260), with a fine Cartesian LGR around the wellbore to reduce numerical artifacts around the wellbore (total cell count with LGR=1,327,200). The model consists of two facies. All simulations were performed without including wellbore dynamics or mechanical skin.
The production cuts initiated last December by some of the world’s largest crude producing nations will continue for at least another 9 months. The decision was announced Thursday in Vienna, Austria at the headquarters of the Organization of the Petroleum Exporting Countries (OPEC). The extension, which begins 1 July, holds in place an agreed reduction of 1.8 million B/D, or about 2% of global production, that OPEC leaders said was met with 102% compliance in April. Non-OPEC nations, including Russia, are expected to take part in the new round of cuts. Maintaining lower output through the first half of this year has been cited as a major factor in supporting global crude prices at around USD 50/bbl.
The production cuts initiated last December by some of the world’s largest crude producing nations will continue for at least another 9 months. The decision was announced Thursday in Vienna, Austria at the headquarters of the Organization of the Petroleum Exporting Countries (OPEC). The extension, which begins 1 July, holds in place an agreed reduction of 1.8 million B/D, or about 2% of global production, that OPEC leaders said was met with 102% compliance in April. Non-OPEC nations, including Russia, are expected to take part in the new round of cuts. The move has also been viewed as a driving force behind renewed US exploration activity in unconventional oil fields.
ABSTRACT: The 27.3 km long Semmering Base Tunnel with deep access shafts will be the third longest railway tunnel of Austria. The overburden depth is between 40 m and 800 m. The tunnel construction is divided into three lots. From the view of design and geotechnics, the project has many challenges. Overall more than 40 ground types were defined. The tunnel runs through many fault zones. Measures against squeezing, swelling and flowing ground have been designed. The carbonate rocks are partly karstified with a large groundwater reservoir. Extensive pregrouting works from up to 300 m long horizontal directional drillings are foreseen in order to reduce the predicted entering groundwater volume from up to 300 l/s and to protect the groundwater reservoirs. In accordance with the Austrian guideline for conventional tunnelling, a detailed geotechnical design was carried out.
1 GENERAL OVERVIEW
The Semmering Base Tunnel (SBT) is situated in Eastern Austria and is part of the Baltic-Adriatic Corridor, which is one of the most important cross-Alpine lines in Europe. Based on extensive geological investigation in the station and alignment selection procedure and environmental impact assessment a detailed tender design was possible (Gobiet & Nipitsch 2015). Therefore, the driving method could be selected and furthermore various important technical, geotechnical, structural and environmental measures could be taken into account on time (Ekici et al. 2011). The tunnel is about 27.3 km long and is being driven from the portal at Gloggnitz and three additional intermediate construction accesses in Göstritz, in the Fröschnitzgraben and in Grautschenhof. For reasons of organization, scheduling and topography, the tunnel is divided into three construction lots (Gobiet & Wagner 2013). The eastern contract “SBT1.1 Tunnel Gloggnitz” is under construction since the middle of 2015 (Wagner et al. 2015), the middle contract “SBT2.1 Tunnel Froschnitzgraben” started at the beginning of 2014 (Daller et al. 2013) and the western contract “SBT3.1 Tunnel Grautschenhof” will follow in spring of 2016 (Klais et al. 2015).
Subject of this article is the methodology of the geotechnical design for the entire tunnel system. The geotechnical design work started with the commissioning of the project in early 2005 and was done step-by-step more in detail in every design phase of the project.
ABSTRACT: At the construction lot SBT2.1 of the Semmering Base Tunnel (SBT) in Austria two shafts with a depth of about 400 m were excavated following the principals of the new Austrian tunneling method (NATM). In the design phase several numerical calculations were carried out to dimension the necessary support measures based on different geological and geotechnical circumstances. During construction it was the aim to compare the actual system behavior with the one of the design. Therefore, a comprehensive monitoring program including 3D-displacement monitoring, extensometer measurements and strain gauges was performed. The monitoring results have to be interpreted based on a mechanically correct model representing geological and geotechnical conditions in reality. Therefore, it was necessary to take a transversely isotropic material behavior into account. Depending on the horizontal in-situ stresses a good match of the calculated and the observed displacement pattern was found.
The Semmering Base Tunnel (SBT) is situated in Eastern Austria and is part of the Baltic-Adriatic Corridor, which is one of the most important cross-Alpine lines in Europe (http://www.baltic-adriatic.eu/en/baltic-adriatic-axis/corridor-1).
The tunnel is about 27.3 km long and is excavated from the portal at Gloggnitz and three intermediate construction accesses in Göstritz, in the Fröschnitzgraben and in Grautschenhof. The main elements of the tunnel system are the two single-track running tunnels between Gloggnitz and Mürzzuschlag, cross-passages with a maximum spacing of 500 m and an emergency station near the center of the tunnel with two permanent ventilation shafts. For reasons of organization, scheduling and topography, the tunnel is divided into three construction lots (Gobiet & Wagner 2013). Further information on the SBT and SBT2.1 has already been published (e.g. Daller et al. 2013).
Subject of this article are the two shafts “Fröschnitz 1” and “Froschnitz 2” of the construction lot SBT2.1 “Tunnel Froschnitzgraben” which has been under construction since 2014.
The shafts enable the supply to and disposal of materials from the tunneling works of the two single-track running tunnels and the emergency station. In the final state they will serve as air supply and extraction shafts in case of an incident.
The paper presents findings of a case history based on the first application of specialized organic fibre lost circulation materials (LCM) in Europe. It lists technical challenges encountered during the recent drilling of HPHT exploration well Stripfing T1 to 6022 mMD and describes how new fibrous organic LCM have proven their value in a range of lost-circulation applications in the Vienna basin. The paper will also elaborate on the narrow mud window available and the main drivers for well design along with contingency concepts.
The operator identified an innovative LCM which had the characteristics that it is plastic, deformable and can be squeezed into a loss zone resulting in an effective seal being formed across the loss zone with an internal filtercake rather than a high loss filtercake forming on the exterior of the wellbore. Several pills containing this product were used achieving excellent results when applied according to a specific procedure. The paper will look in detail at this procedure and highlight the input from detailed decision-tree charts, and the characteristics and wettability of fibres.
The Vienna Basin has a history of mud losses ranging from continuous seepage to severe losses. The main concerns while planning the Stripfing T1 well were the magnitude of overpressure in combination with the expected losses. The above had been the root cause of previous failures.
Several attempts to cure the losses with standard LCM had proven unsuccessful, as a consequence the operator decided to adopt a new approach using a specialized LCM product in order to avoid running casing earlier. Successful implementation of this advanced technique allowed the operator to drill the well using only 3 casing strings and a final hole size of 8 ½ in. without reducing the mud weight.
The level of success achieved by using these materials suggests it should be considered as the preferred standard practice for curing any type and volume of losses.
For infrastructure projects with shallow overburden a comprehensive geotechnical monitoring program and its implementation in the daily operation is essential for a successful and safe completion of the works. A continuous control of both the tunnel and the surface according to the observational method within a strict geotechnical safety management is one of the most challenging tasks for such projects. The paper gives a short overview about the geotechnical design and monitoring at the large OeBB railway project Lainzer Tunnel lot LT 31 in Vienna/Austria. Two case histories shall illustrate the implementation of the geotechnical safety management.
Core of the OeBB Lainzer Tunnel project with 12.8 km is lot LT31, having a length of 3.6 km, where residential areas and major traffic infrastructure are situated along the tunnel route (see Figure 1).
The tunnel was constructed as a double-track tube with an excavation cross-section of about 130 m² using NATM. Due to the hydrogeological conditions dewatering and groundwater relaxations in advance to the excavation were necessary. Excavation started from the shafts at “Klimtgasse” and “Lainzerstraße” in both directions. 2/3 of the tunnel alignment follows a major railway line (“Verbindungsbahn”) under operation. The overburden ranges from approx. 6 m (southern part) to 26 m in the soft ground sections and to approx. 55 m (western part) in the bedrock region. Due to the difficult geotechnical conditions and the potential direct impact of the project activities on the public, a Geotechnical Safety Management Plan (GSMP) including a comprehensive monitoring concept was established and strictly followed (Moritz et al. 2011).