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Collaborating Authors
Open hole/cased hole log analysis
Inversion-Based Workflows For Interpretation Of Nuclear Density Images In High-Angle And Horizontal Wells
Shetty, Sushil (Schlumberger) | Omeragic, Dzevat (Schlumberger) | Habashy, Tarek (Schlumberger) | Miles, Jeffrey (Schlumberger) | Rasmus, John (Schlumberger) | Griffiths, Roger (Schlumberger) | Morriss, Chris (Schlumberger)
ABSTRACT: We have developed multi-step inversion-based workflows for the interpretation of nuclear density images in high-angle and horizontal wells. The key component of the workflow is the model-based parametric inversion using a newly developed fastforward model based on second-order 3D sensitivity functions. For the first time, a layered formation model and borehole are included simultaneously in the analysis resulting in accurate layer thicknesses, shoulder-bed corrected layer densities, and borehole geometry consistent with all the data. The parametric model used for interpretation includes a multi-layer dipping formation, mud properties, borehole geometry, and 3D well trajectory. Measurement sensitivities are used in the design of a flexible and robust four-step iterative procedure for determining optimum parameter values. In the first step of the procedure, an initial guess for the formation layering and dip is derived from the compensated density measurement by extracting sinusoidal features of the image and squaring the bottom quadrant profile. In the second and third steps, the optimum mud properties and borehole geometry are derived from the shallow sensing measurements. In the final step, the optimum formation layering and dip are derived from the deeper sensing measurements. The workflow utilizes an adaptive sliding window whose length is determined after segmentation of the images along the trajectory based on the relative dip. The workflow is especially tuned for interpretation in horizontal wells, when potential ambiguity in interpretation is increased because of the difficulty in determining the dip, lateral changes in layer properties and the influence of stand-off and nearby non-crossed boundaries. In scenarios where the wellbore trajectory is nearly parallel to the boundary, the parameterization includes the non-crossed boundaries. The inversion window size is small and the processing enforces the lateral continuity of the layer thickness or formation densities locally.
- Europe (0.98)
- North America > United States > Texas (0.28)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > Block 30/6 > Veslefrikk Field > Statfjord Group Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > Block 30/6 > Veslefrikk Field > Dunlin Group Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > Block 30/6 > Veslefrikk Field > Brent Group Formation (0.99)
- (3 more...)
- Well Drilling > Well Planning > Trajectory design (1.00)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
ABSTRACT: Pauto Complex is part of a series of imbricated thrust sheets developed as result of the Colombian Eastern Cordillera uplifting. Mirador Formation is the producer rock being very homogeneous and clean quarzoarenite very continuos through and across the entire field. The structure has been interpreted as elongated NE-SW asymmetric anticlines bounded by east verging fore-thrust and associated back-thrust that runs parallel to the structure axis. Tectonism and a deep depositional environment played a strong role on the rock deformation and diagenesis, resulting in a very complex structural and rock quality system, where both the matrix and the natural fractures contribute to well productivity. The present work is focused on defining a methodology that allows a reliable estimation of the basic parameters of the petrophysical model (Net sand, Net Pay, Fluid Saturations, Porosity, and Permeability to support both the in-place volumes (GIIP and OIIP), and the well productivity for the Pauto Complex). The methodology is based on the integration and understanding of all available data with emphasis on the capillary pressures, core fluorescence, and well production. INTRODUCTION Pauto Field is a rich gas condensate field that produces from Mirador Formation and despite of low porosity and matrix permeability, average rates per wells exceed 2000 bopd and 30mmscfd. Although, natural fractures are present in the system, there is evident that matrix contributes as well. Pauto petrophysical model is based on extrapolated properties of the nearest field in the area (Cupiagua Field). Considering this difference and also that predicting rock quality has a direct impact on well productivity and reserves estimation, it is important to build a specific petrophysical model which includes the available core and log data in the Pauto Complex, and reflects the unique rock quality and heterogeneities of the reservoir.
- Geology > Sedimentary Geology (0.88)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.48)
- South America > Colombia > Mirador Formation (0.99)
- South America > Colombia > Casanare Department > Pauto Field (0.99)
- South America > Colombia > Casanare Department > Llanos Basin > Cupiagua Field (0.99)
- South America > Colombia > Casanare Department > Florena Field (0.99)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- (2 more...)
ABSTRACT: Recent wells drilled by an operator offshore Brazil provided the opportunity to perform a direct comparison of multi-mineral formation evaluation using as input either traditional Wireline (WL) or Logging While Drilling (LWD) data. The principal target was an Albian carbonate reservoir of the Quissamã Formation. This formation has a complex lithology with variable amounts of dolomitization and presence of quartz and clay. Computing a correct matrix density and characterizing the rock texture for producibility estimation is critical. Initially a 12.25 inch diameter vertical pilot well was drilled with Synthetic Oil Based Mud (SOBM) and logged using basic LWD tools (resistivity / density / neutron). A complete WL program followed for a better understanding of reservoir characteristics. The logging program included induction, neutron-density, nuclear magnetic resonance (NMR), elemental spectroscopy, formation pressure measurements and fluid samples. In spite of unknown formation water salinity it was relatively straight forward to identify a formation water resistivity value consistent with log responses over the lower reservoir section. Resistive invasion patterns clearly indicated the permeable intervals below the free water level, confirmed by the NMR T2 distribution profile. Pressure gradients and fluid samples demonstrated the validity of the analysis. In order to explore reservoir connectivity and facies variation at some distance from the vertical hole the pilot well was side-tracked using an "S" shape trajectory with a maximum inclination of 55 degrees. The side-track borehole was drilled with an 8.5 inch bit size with the same type of SOBM, using a BHA which included rotary steering assembly, multi-function measurement tool and LWD NMR tool. The LWD measurements allowed the formation evaluation analysis performed in the pilot well to be replicated. Capture cross-section (or Sigma) may be sensitive to the invaded zone due to its shallow depth of investigation, while 2 MHz resistivities read far beyond.
- North America > United States (0.93)
- South America > Brazil > Rio de Janeiro (0.29)
- Geology > Mineral (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.35)
- South America > Brazil > Campos Basin (0.99)
- North America > United States > Alabama > Moscow Field (0.89)
- Well Drilling > Drilling Measurement, Data Acquisition and Automation > Logging while drilling (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Improving Geologic Core Descriptions And Heterogeneous Rock Characterization Via Continuous Profiles of Core Properties
Suarez-Rivera, Roberto (Schlumberger Innovation Center) | Edelman, Eric (Schlumberger Innovation Center) | Handwerger, David (Schlumberger Innovation Center) | Hakami, Ahmed (Saudi Aramco) | Gathogo, Patrick (TerraTek, A Schlumberger Co)
ABSTRACT: Unconventional tight shale reservoir systems are heterogeneous at all scales. This results from multiple sequences of deposition and accumulation of sediments in time, followed by locally varying and extensive post-depositional transformations. It has been said that the textural variability in shales at the thin-section scale rivals the variability of an entire outcrop in sandstones (J. Schieber). Given their colloidal size of organic and inorganic sediments, their large surface area to volume ratio, and their high chemical potential for undergoing geochemical transformations, the resulting distribution of material properties in tight shales is highly heterogeneous. Understanding scale-dependent heterogeneity in tight shales and other unconventional reservoirs is important for hydrocarbon production and recovery. It is also important for characterization, modeling, and for extending our observations, experience and understanding from one scale (e.g., core-scale) to another (e.g., log- or seismic-scale). The presence of scale-dependent heterogeneity also poses additional important questions regarding sampling for characterization, including the number of samples needed, the adequate scale for sampling and others. Addressing and solving these questions will lead to significant progress on tight shale exploration and efficient production. This paper describes continuous measurements along the length of the core that result in significant improvements to geologic core descriptions and heterogeneous rock characterization. Using multiple high-resolution measurements (e.g., of strength, thermal conductivity, CT atomic number, and XRF mineralogy) we define the principal rock classes, with similar characteristic properties, that define the heterogeneous system. The thickness and cyclic stacking patterns of these units provide quantitative information of the depositional system and its sequences. The method also differentiates transitional contacts from abrupt contacts, and provides additional information for developing a geologic model. Although the cyclic nature of tight shale sequences is often visually apparent, the variability in properties within these sequences is only accessible by the continuous measurements.
- North America > United States (1.00)
- Asia > Middle East > Saudi Arabia (0.69)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
ABSTRACT: The reservoir rock characterization is essential for definition of exploitable hydrocarbon content zone, identifying storage and flow capacity. Therefore a methodology was designed adapted to characteristics and conditions of Cerro Negro field. The Cerro Negro field is located in Carabobo block at the Orinoco Belt Oil, in basin eastern Venezuela, characterized by unconsolidated sands and extra heavy oil. The methodology applied is based on integration different rock characterization techniques : rock type determination by the cluster analysis, Winland and Pittman method's by pore throat size, additionally, it was applied the Kozeny-Carman equation's to determine rock quality index (RQI) and flow zone index (FZI) and obtain the hydraulic units. The aim of apply several techniques is to use the most of the available data, for crosscheck and adjust the rock types differentiated over the column the hydrocarbon, to decrease the uncertainty related to the reservoir rock quality and the hydraulics units. Moreover, the results were validated with vertical and horizontal wells production tests. The study was carried out with 93 vertical wells of the field, among them, 8 wells with conventional and special core analysis. The petrophysics properties (porosity, permeability and water saturation) were obtained through conventional deterministic evaluation (log interpretation), calibrated with core data and mercury injection capillary pressure (MICP). Cerro Negro Field is located in Carabobo Block in Orinoco Heavy Oil Belt at Eastern Venezuela Basin, reservoirs are characterized by unconsolidated sand with extra heavy oil of 8 API (Figure 1). The stratigraphic framework is represented from the base to the top is: Oficina Formation (aged Early Miocene), Freites, Formation, Middle Miocene, Las Piedras Formation (aged upper Miocene) and Mesa Formation (aged Pleistocene-Pliocene). The producing interval is the Morichal Member of Oficina Formation, Morichal Member is divided operationally in three units: Upper Morichal, Middle and Lower Morichal.
- South America > Venezuela > Anzoátegui (1.00)
- South America > Argentina > Santa Cruz Province (1.00)
- South America > Argentina > Mendoza Province (1.00)
- (2 more...)
- Geology > Geological Subdiscipline > Stratigraphy (0.35)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.30)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Core analysis (0.87)
ABSTRACT: Uncertainty analysis for petrophysical parameters is important for well planning and stimulation decisions. This process is especially demanding for unconventional reservoirs. The complex factors include rock lithology variations and field production history. Pulsed neutron tools (PNT) play an important role in the monitoring of production wells with cased completion. In saline formation water environments, the thermal neutron capture cross section (Sigma) measurement discriminates between water, gas, and oil. When the formation water salinity is low or varies as a result of flooding stimulation, the spectroscopy measurement of carbon and oxygen ratios (C/O) often leads to accurate residual oil saturation analysis, especially for reservoirs with medium to high porosity. With the recent development of the multi-detector PNT (MDPNT), case studies have been reported for gas saturation and depletion analysis in tight gas reservoirs. The accuracy of the reservoir saturation analysis with MDPNT depends on accurate rock lithology and porosity determination. When core data or openhole logs are not available, the MDPNT can be used to estimate these parameters and to obtain a standalone evaluation of porosity, lithology, and saturation. The results may be affected by errors resulting from statistical tool responses and measurement dynamic ranges. This paper presents results from a comprehensive study and proposes a framework to quantify uncertainty from these error sources. BACKGROUND Pulsed-neutron tools (PNT) have been used for several decades to provide water saturation estimates during well life-cycle. The introduction of PNT logging more than four decades ago (Wahl et al. 1970; Youmans et al. 1964) provided the first through-casing measurement of formation water saturation. A few years after introduction of PNT, the development of C/O logging using pulsed neutron technology solved the problem of saturation determination in freshwater reservoirs (Lock and Hoyer 1974; Schultz and Smith 1974), although somewhat less robustly.
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
ABSTRACT: The problem of deducing lateral extent of sedimentary bodies of interest drives the need for a detailed depositional facies interpretation. Manual interpretation can be time-consuming and differences between interpretations made by different experts can be difficult to resolve. Automated facies interpretation methods can overcome some of these problems, but agreement between the experts' interpretation and that of the machine can be difficult to attain. Borehole resistivity images contain structural and stratigraphic information in addition to a high-resolution shallow resistivity measurement, thus offering a multitude of interpretation possibilities. A new semi-automated classification method for borehole resistivity images, called Statistical Analysis of Image Logs (SAIL), may help bridge the gap between different interpretations. SAIL is based on distributions of microresistivity and on calculating a set of variability coefficients for various scales for every point of the image, whereby the distributions of this data in the interval studied are matched to the corresponding distributions of data from facies training samples, picked in regions of calibration with core. The user involvement might be as minimal as finding a single short image sample per facies to serve as a facies training sample. With its options for lithofacies and depofacies classification, this method improves multiscale visualization and has unique capabilities to help align petrophysical and geologic interpretation. In this study, we illustrate an application of this classification method for borehole resistivity images to predict core depofacies in a deepwater depositional environment. The application consists of a three-stage process: in the first two stages, the semi-automated borehole image classification method is applied to predict a fine and a coarse sequence of facies blocks, while in the third stage, a set of geologic-based rules is applied to the two image classifications and an electrofacies classification from open-hole logs, to produce a depofacies prediction.
- Geology > Geological Subdiscipline > Stratigraphy (0.90)
- Geology > Sedimentary Geology > Depositional Environment (0.67)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.31)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- North America > United States > Texas > East Gulf Coast Tertiary Basin > Wilcox Formation (0.99)
- North America > United States > Mississippi > East Gulf Coast Tertiary Basin > Wilcox Formation (0.99)
- North America > United States > Louisiana > East Gulf Coast Tertiary Basin > Wilcox Formation (0.99)
- North America > United States > Gulf of Mexico > East Gulf Coast Tertiary Basin > Wilcox Formation (0.99)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Borehole imaging and wellbore seismic (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (1.00)
Borehole Acoustic Reflection Survey (Bars) From Modern, Dipole Acoustic Logs For High-Resolution Seismic-Based Fracture Illumination And Imaging
Grae, A.D. (Shell Exploration & Production Company) | Ugueto, G.A. (Shell Exploration & Production Company) | Roberts, C.J.A. (Schlumberger) | Yamamoto, H. (Schlumberger) | Oliver, T. (Schlumberger) | Martinez, G. (Schlumberger)
ABSTRACT: Understanding the impact of natural fractures in unconventional plays has been limited by the difficulty of describing fractures and intergrading this information from different scales. On one end of the scale, we have information from seismic that can allow the visualization of large fault systems or highlight areas of high tectonic displacement. On the other end of the spectrum, the data provide from wells, image logs, core and production can allow one to map and even characterize the fractures that intersect with the wellbore. What has been missing is data that allows bridging of the gap between the large scale, as provided from seismic, to the meso- and microinformation provided by logs and core. However, with modern borehole acoustic tools, meticulous data acquisition and adaptive processing algorithms, we can generate a borehole acoustic reflection survey (BARS), thereby creating a high-resolution seismic image of fractures around the well. To accomplish this, the components of the acoustic waveform data that escape the wellbore area and are reflected off the fractures are separated and processed using new, innovative processing methods. This paper discusses the tool and subsequent processing that enables the application of this technology in unconventional reservoirs. Moreover, the paper then describes the integration and verification of this data with seismic, borehole image data, and conventional core. Finally, the paper lays out conclusions and data acquisition modifications to better leverage the complimentary BARS data. INTRODUCTION As oil and gas exploration and development moves further into unconventional plays, natural fracture detection and characterization has become more important. Some plays can leverage these natural fractures to increase a well's productivity, while in other plays the fractures can be a hindrance, acting as loss zones or creating high leakoff during fracture stimulation.
- South America (0.68)
- North America > United States > Colorado > Denver County > Denver (0.15)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.68)
- Geology > Petroleum Play Type > Unconventional Play (0.68)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
ABSTRACT: "Anomalous" LWD propagation resistivity log responses were observed in a high angle well. The anomalous character includes anomalous curve separations, periodic variations with depth, and anticorrelation of the phase and attenuation apparent resistivity curves. In particular, the long-spacing curves show larger depth variations than the short spacing curves. It was also observed that the cyclic variations remain in either compensated or uncompensated logs. The section of the well was drilled with oil-based mud in a shale formation. Several possible hypotheses were tested to explain the log. Numerical modeling showed that resistivity anisotropy, tool eccentering, thin beds or dielectric effects alone could not explain the curve separations and the anticorrelation of the attenuation and the phase difference apparent resistivity log responses. To test the hypothesis of spiraled borehole effect, a detailed 3D numerical study was performed. Contrary to an earlier anticipation, a spiraled borehole itself does not necessarily cause significant cyclic log variation. Spirals gouges of reasonable geometrical dimensions failed to reproduce the magnitudes of variations in depth as observed in either the attenuation or phase difference logs, particularly for long spaced arrays. It is discovered that only a combination of a spiraled borehole with resistivity anisotropy, and optionally including tool eccentering effect, can explain the observed anomalous log responses, consistent with the anisotropic shale lithology. The numerical study further revealed that the alternation of the maximum and minimum responses in the logs does not depend on the transmitter-to-receiver or receiver-to-receiver spacing, but rather on the spiral period, which explains the long- and short-spaced logs having closely similar period. Simulations in geometrically same spiral models, with and without anisotropy indicate an "amplification" of the spiral affects with inclusion of anisotropy in the formation model. Formation anisotropy can "amplify" spiral effects, which are normally a minor perturbation for apparent resistivity responses.
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
ABSTRACT: Borehole geometry is a critical measurement. Irregularities of the borehole wall indicate the location and severity of rock failure, which offer precious information on the level of in-situ stresses and the strength of the formation. Precise borehole geometry can be used to increase the accuracy of environmental corrections of logging while drilling measurements. Borehole geometry can be obtained in real-time from acoustic transducers mounted on the bottom hole assembly (BHA). These transducers calculate their distance from the borehole wall by measuring the time the sound wave travels such a distance. During drilling, the acoustic transducers rotate with the BHA and scan the entire azimuth of the borehole. If the BHA is stationary inside the borehole, such a scan can give the precise borehole geometry. Since the BHA usually moves laterally inside the borehole as the result of the drilling operation, this motion creates a challenge when interpreting the data for information on borehole geometry. In this paper, the authors propose an algorithm that iteratively eliminates the effect of BHA lateral motion to obtain precise borehole geometry. It does not make any assumptions with regard to the shape of the borehole, and it can be applied to any number of acoustic transducers (minimum three) that are arbitrarily oriented. INTRODUCTION The geometry of the borehole is one of the most essential measurements while drilling. Borehole geometry can be used to correct the sensor measurements for the effects of standoff (for example, Schultz et al., 1998; Minette et al., 1999). Mechanical failure of the formation creates irregularities around the borehole. The orientation and shape of borehole irregularities are essential for geo-mechanical studies of the borehole (Zoback, 2007). A precise knowledge of the borehole geometry is also useful in estimating the cement volume for completion.
- North America > United States (0.47)
- Europe > United Kingdom (0.28)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (0.71)
- Well Drilling > Drilling Measurement, Data Acquisition and Automation > Logging while drilling (0.49)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.48)