Quasi K-orthogonal grid generation is presented, to improve grid quality and method stability with respect to flux approximation in the presence of strongly anisotropic full-tensor permeability fields.K-orthogonal grid generation is only possible for low anisotropy ratios. Quasi K-orthogonal grid generation involves satisfying the K-orthogonal condition approximately, resulting in grids that place less demand on an approximation with respect to stability conditions, and therefore improve grid quality with respect to flux approximation in the presence of anisotropic permeability fields. The method employed enables Delaunay grid generation principles to be employed in a locally transformed system according to local permeability tensor variation. The resulting method has great flexibility for handling complex geometries and can handle jumps in permeability tensor principal axes orientation and jumps in coefficients and details will be presented. Results are presented that demonstrate the benefit of a quasi K-orthogonal grid. Highly challenging cases involving strong full-tensor permeability fields where control-volume distributed multi-point flux approximation (CVD-MPFA) schemes exceed their stability limits and yield solutions with spurious oscillations when using conventional grids, are solved using the new grid generation method. CVD-MPFA schemes are still required as the grids are only approximately K-orthogonal in such cases, however the schemes retain a discrete maximum principle on the new quasi-K-orthogonal grids and yield well resolved solutions that are free of spurious oscillations. While the two-point flux approximation (TPFA) requires strict K-orthogonality, results using both CVD-MPFA and TPFA will be presented. New Quasi K-orthogonal grid generation methods are presented that satisfy the K-orthogonal condition approximately, resulting in practical grids that restore a discrete maximum principle (stability) for the CVD-MPFA schemes when applied to cases involving general full-tensor permeability fields. Results are presented for a variety of test cases that confirm the validity of the grids.
ABSTRACT: Flow characteristics of fracture networks are of great interest in applications in reservoir engineering. Assessing these characteristics requires in general significant efforts in conducting finite element analysis and then adapting the results by means of upscaling techniques to the entire reservoir. The use of commercial or other proprietary software for modeling these characteristics has been widely reported in the literature. While well developed, researchers might find the difficulty of access to the software or to the source codes. We aimed to address these difficulties by proposing a simple solution for modeling fluid flow through fractures in two and three-dimensional DFN models implemented in an open source package, built on a new hybrid mesh-pipe model. It is demonstrated that the proposed method is accurate and efficient. The application of our proposed method for the directional permeability analysis of DFN models is also discussed.
We present a triangulation-based technique to compute both the gravity and gravity gradient effects due to relief of both topography and bathymetry. Computing such effects is a computationally intensive task and so we turn to adaptive triangulations to represent topography and bathymetry, which are usually delivered in a digital relief model. The resolution of the triangulation adapts according to a combination of the terrain roughness and the decay of gravity with distance from an observation location, under a user specified error tolerance. We use a back propagation approach to split elements in the triangulation to prevent hanging nodes and we insert coastlines as a fixed boundary. As a result, the final triangulated surface is continuous and without artificial vertical sides. Due to the adaptive nature of the discretization, the computational time is greatly reduced. Our technique is applicable to gravity and gravity gradient observations made on land, in air, and at sea. We demonstrate the technique using field examples that cross both land and water.
Presentation Date: Tuesday, September 26, 2017
Start Time: 2:15 PM
Presentation Type: ORAL
Kim, Yonghwee (Baker Hughes) | Boyle, Keith (Chevron) | Chace, David (Baker Hughes) | Akagbosu, Pius (Baker Hughes) | Oyegwa, Akomeno (Chevron) | Wyatt, Dennis (Chevron) | Okowi, Victor (Baker Hughes) | Gade, Sandeep (Baker Hughes)
Copyright 2017, held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors. Annual Logging Symposium held in Oklahoma City, Oklahoma, USA, June 17-21, 2017. ABSTRACT Monitoring fluid saturations in a producing reservoir over time is critical for the effective exploitation of the resources. This can be complex in a two-phase system and is exacerbated when changes in the gas cap due to depletion or contraction, due to re-pressurization from water injection, have to be considered. Consequently, a three-phase reservoir fluid saturation measurement is crucial in determining the future of the reservoir and if remedial actions must be taken for overall optimization of the reservoir's production. To answer this challenge an advanced salinityindependent method that combines the carbon/ oxygen (C/O) analysis with gamma ray ratio-based gas saturation techniques has been developed to deliver three-phase fluid saturations. In this new method, C/O analysis and a gamma ray ratio-based gas saturation method are incorporated using an innovative triangulation technique to simultaneously quantify water, oil and gas saturations. Well-specific Monte Carlo N-Particle (MCNP)-based forward modeling enables pre-job sensitivity analysis and provides the predicted theoretical measurement responses required for log quality checks and formation evaluation in data postprocessing. This paper describes a collaborative effort by an operator and a service company to evaluate the new three-phase formation fluid saturation analysis technique to obtain post-production fluid contact and saturation in a mature field in Nigeria that was put on production in the early 1970s. In this particular well-logging campaign, the objective was to estimate the current hydrocarbon saturation. Because the formation water salinity of the subject field was low (typically less than 15,000 ppm NaCl equivalent), C/O and inelastic gamma ray ratio 1 measurements were acquired. The new triangulation method was used to integrate these measurements to provide salinity-independent three-phase fluid saturations. Results from example wells analyzed using the new technique are presented.
The delineation of three-phase reservoir fluid saturation is important to operators as fields mature. The understanding of multiphase reservoir fluid distribution determines the operator's subsequent reservoir management and production strategies such as infill drilling and reentry planning for bypassed hydrocarbon access, perforation or squeeze interval selection, injection planning, etc.
Pulsed neutron well logging technology enables acquisition of useful data for saturation identification in cased hole environments. Interpretation of pulsed neutron data in three-phase formation fluid conditions has historically involved the use of empirical correlations or corrections to carbon/oxygen (C/O) and pulsed neutron capture (PNC) sigma measurements. However, a robust interpretation technique to provide reliable and quantitative three-phase fluid saturation results under any reservoir conditions (including fresh, saline and variable or unknown formation water environments) has not been available.
This paper presents a new patented interpretation method to quantify three-phase formation fluid saturations using pulsed neutron logging data. The principles of pulsed neutron logging and nuclear physics remain the same; however, the application of a multidetector pulsed neutron tool measurements and an innovative data analysis approach enabled the development of the new interpretation technique. The method combines two measurements recorded by a multidetector pulsed neutron logging tool and integrates Monte Carlo modeling responses to quantitatively determine formation water, oil and gas saturations.
Application case studies from sandstone and carbonate reservoirs are demonstrated. The technique successfully generated multiphase formation saturation profiles in various reservoir scenarios. In addition, the delivered solutions have enabled operators to understand current reservoir fluid saturations and perform subsequent well and reservoir management activities to maximize hydrocarbon production.
Saturation monitoring is a key component that requires special planning of reservoir management in a Water Alternating Gas (WAG) EOR process. Numerous factors have to be taken into account when planning surveillance, from fluids to filling history and compartmentalization. The alternating cycles are also important in determining when and where to gather the data.
Within the WAG EOR process itself, there are field specific drivers that ensure the miscible process delivers an efficient sweep. Quantifying saturation in WAG EOR is extremely challenging. We cannot treat this application as a simple three phase time lapse pulsed neutron problem. The end point values of various nuclear attributes will change with the fluids composition during production of the WAG cycles. Changes in water salinity, oil density, gas composition, pressure variation and deviation from compositional gradients will all potentially modify the notional end points. Access to “minimal” well and reservoir information will secure a robust saturation extraction from the application of multiple nuclear attributes. A more unique solution would require special modes of data acquisition, tool modifications or well conditions.
Well access can be challenging on a number of fronts from production deferral, limitations on personnel on board and costs of data gathering. Applying learnings from previous data gathering campaigns combined with evolving technologies in the area of multidetector pulsed neutron and memory conveyance can make surveillance in WAG EOR an efficient tool for reservoir management.
This is an arena where reservoir engineering and petrophysics needs to work together. This paper presents learnings from a Norwegian field under WAG injection and addresses the data acquisition, interpretation and integration within the reservoir model.
Complexity, size and hostile environmental conditions of plants, refineries and offshore platforms make monitoring and security assurance difficult challenges. Plants and platforms are usually equipped with sensors to monitor pipes, flows, pumps, equipment, rotating machines, valves, tanks, which are often managed by heterogeneous systems, sometimes not accessible via remote connection, but seldom, this real-time monitoring concept is applied to workers.
Due to the high risk in process areas, it’s crucial to:
• provide real time personnel location to Control Room operators, Search and Rescue Teams, Safety Department, so to assure workers’ safety and incident prevention. Mainly considering that in many cases, the platforms contain facilities to house the workforce as well.
• ensure that personnel does behave according to prescriptions
In this paper we describe our solution based on a real-time Automated Tracking System [ATS], based on a 3D representation of reality accessible via web browser on computer or mobile devices, configurable on any platform’s, plant’s, refinery’s.
Measurement of rock mass discontinuities was the key for rock mass 3D network simulation, seepage analysis, and stability analysis. In this paper, a non-contact rock mass discontinuities detection method based on the single camera binocular three-dimensional reconstruction theory was presented. This method provided an effective way for grouping rock mass discontinuities and calculation the discontinuity orientations. The main flow of the method was: (1) obtaining three dimensional point cloud data based on the binocular three-dimensional reconstruction theory by single camera, (2) de-noising and re-sampling on point cloud data before triangulation to reduce holes in the reconstructed triangular mesh, (3)grouping rock mass discontinuities automatically based on an improved K-means algorithm which adopted density and clustering validity indexes, (4) segmenting the discontinuities in the same group based on the angle and the adjacent relationship between two triangular facets, and (5) fitting the segmented point cloud using the Random Sample Consensus (RANSAC) algorithm and calculating its orientation. This method was applied to the grouping and measurement of discontinuities of a rock mass slop. The results showed that the grouping and measurement of discontinuities were reliable and of high accuracy that could meet the engineering requirements.
Volumes of rock contain a wide range of ‘planes of weakness’ at all scales, each with a statistical distribution of spacing and orientation (Goodman, 1989). In rock engineering, these planes of weakness are generally referred to as ‘discontinuities’. It is essential to characterized is continuities geometry properties at exposed rock faces in permeability studies for hydrological, mechanical behaviour assessment and in the engineering design of man-made structures placed in or on rock masses.
Abstract: This paper investigates how 3 dimensional (3D) laser images of rock faces can be processed to highlight several characteristics of the rock mass in three different geological environments. The first scene features large cubic quartzite rock blocks from a road cut. The second scene shows a layered sedimentary sequence composed of massive limestone and more friable dolostone from a quarry. The third scene exhibits shatter cone structures imprinted in an outcrop in the Subdury impact crater, in northern Ontario. Images are acquired using a triangulation laser camera with a 30° × 30° field of view, mounted on a tripod, at distances ranging from 1 to 3 m. Epsilon nets (ε-nets) are used to downsample the point cloud data with little loss to the overall structure that they represent. A 2.5D triangular irregular mesh (TIN) is constructed from the 3D point cloud data using a delaunay triangulation and smoothed using a few iterations of the geometric laplacian. Three different processing strategies are tested to enhance the visual perception of fracture orientation and surface roughness: color-coding of strike and dip, curvature analysis and outer normal planar clustering.