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Collaborating Authors
Well Drilling
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: Tight unconventional reservoirs have become an increasingly common target for hydrocarbon production. Exploitation of these resources requires a comprehensive reservoir description and characterization program to estimate reserves, identify properties which control production and account for fracturability. Multiscale imaging studies from the whole core to the nanometer scale can aid in understanding the multiple contributions of heterogeneity, natural fracture density, pore types, pore throat connectivity, mineral and organic content to the petrophysical response and production characteristics. In this paper we present three examples of the application of multiscale imaging to challenging unconventional reservoirs; a deep clastic tight gas reservoir, a fractured basement reservoir and coal seam gas reservoir. All of these samples exhibit features at multiple scales which present major challenges to petrophysical evaluation. In all cases heterogeneity and geological rock typing is undertaken at the core scale. FIBSEM imaging can then used to reveal the nanoporous microstructure of the key intervals within the phases of the core material. Petrophysical properties (porosity, permeability, elastic moduli) can also be computed for each key phase and the data upscaled using standard techniques. The presented case histories demonstrate that multiscale imaging and modelling provides a quick complimentary method to characterize the distribution and nature of different pore types and matrix components to characterize the elastic and dynamic rock properties even on rock fragments that are not suitable for conventional core analysis. Moreover the results have the potential to enhance our understanding of petrophysical, fracturing and multiphase flow processes in challenging unconventional reservoirs with low porosities and permeabilities. INTRODUCTION In recent years significant progress has been made in the development of high resolution 3D tomographic imaging and registration techniques to directly image rock microstructures across a continuous range of length scales (from nm to cm scales).
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.68)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.35)
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)
Landing A Well Using A New Deep Electromagnetic Directional Lwd Tool. Can We Spare A Pilot Well?
Netto, Paulo (Petrobras) | Vieira da Cunha, Antonio Mainieri (Petrobras) | Gonçalves Meira, Ana Augusta (Petrobras) | Schmitt, Gustavo Henrique (Petrobras) | Seydoux, Jean (Schlumberger) | da Silva, Augusto Carvalho (Schlumberger) | Chow, Stephanie (Schlumberger) | Guedes, Ana Beatriz Felício (Schlumberger) | Legendre, Emmanuel (Schlumberger) | Mirto, Ettore (Schlumberger) | Samaroo, Rajeev (Schlumberger) | Salim, Diogo (Schlumberger) | Silva, Charles (Schlumberger)
ABSTRACT: Successful placement of a horizontal well requires accurate landing of the well in the desired position and orientation in the reservoir. Operators face operational and economic challenges in achieving accurate landing due to limited seismic resolution, in addition to uncertainty in the reservoir position, orientation, and overall geological structure. These challenges are further amplified by the increasing geological complexity of the reservoirs being drilled today. The current industry practice for landing a well is to use real-time logging while drilling (LWD) measurements to detect expected signatures or markers before entrance into the reservoir (Clark 1988). By comparing offset well data and geological models, these relatively shallow depths of investigation LWD measurements are used to indirectly infer the location and orientation of the "sweet spot". As the target interval is not imaged directly, the well trajectory adjustments may not result in optimal placement of the well for the horizontal section. To check the validity of geological models for landing calculations, operators frequently drill pilot wells to delineate the local reservoir features and at the same time collect petrophysical data to facilitate reservoir characterization. A sidetrack is then drilled to land the well based on the assumption that the reservoir structure does not show significant lateral changes from the pilot well. Drilling a pilot well is both costly and risky especially when drilling in deeper waters where operating costs are high (Ayodele 2004). Following a earlier prototype design of a non-directional resistivity tool (Seydoux, 2004), a new deep directional electromagnetic (EM) LWD service with a radial depth of investigation in the order of 30 m (100 ft) has been introduced in Brazil. The 8.25 in. diameter tool (for 12 ¼ to 14 in. hole sizes) addresses landing applications and structure delineation.
- South America > Brazil (1.00)
- North America (1.00)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (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)
ABSTRACT: Under a long term research area on Advanced Mud Logging (AML) we have further developed some AML methods and techniques, built an integrated AML unit, and completed field testing in several typical Saudi Arabian settings. AML can deliver integrated, comprehensive Petrophysical Information Logs (PILs) as a first aid for well evaluation, and facilitates improved monitoring and thus optimisation of drilling operations. As part of the development process, extensive laboratory tests were performed to validate and compare results of different types of instruments which could be used. In parallel, well site suitable technical operating procedures and appropriate software were developed, to ensure the large amount of tasks to be done can be completed under normal drilling operations time constraints. During the extended pilot testing period, almost all types of wells were included in the programme: wild cat exploration and mature development, gas, oil and water wells, as well as vertical and horizontal wells. AML well site techniques now well established include:high frequency, improved accuracy monitoring of all drilling related parameters; enhanced cuttings image acquisition and processing; direct measurements on cuttings, including grain density, porosity, spectral Gamma Ray (GR), Nuclear Magnetic Resonance (NMR), X-ray diffraction (XRD), X-ray Fluorescence (XRF); and sophisticated mud gas analysis capabilities. We illustrate the power of AML techniques with examples from the above mentioned areas, including excellent matches with acquired wireline logs, unequivocally demonstrated added value for drilling operations, both well control and drilling optimisation, and AML providing petrophysical evaluation information where conventional systems simply cannot measure the parameters required for a complete evaluation. The pilot test results clearly prove AML‟s technical capabilities and indicate many potentially very valuable application areas, including especially challenging shale-gas and shale-oil evaluations.
- Geology > Mineral (0.95)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.45)
- Well Drilling > Drilling Operations (1.00)
- Well Drilling > Drilling Measurement, Data Acquisition and Automation > Mud logging / surface measurements (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Abstract: A series of cases are presented showing how a wider range of hydrocarbon gases detected in Real-Time improves the accuracy of formation evaluation while drilling, in terms of identification of formation fluids contacts and fluid characterization. The results have been obtained with a chromatograph exploiting the benefits of FID technology, optimized for the high resolution detection of heavier hydrocarbon gas components, thanks to a dedicated chromatographic system. Flame Ionization Detector (FID) technology is not new to gas detection on the field; however it had never been applied on the field to the detection of gases heavier than n-pentane. The components analyzed by the system span from n-hexane to toluene. The instrumentation has been run on a number of wells in different fields and countries, and it has operated as a complement of an advanced surface logging system. Unlike other technologies presently utilized for this scope, this system reduces the required equipment and personnel to a minimum. The reliability of the system has also been quantified in this paper, with a procedure that the authors propose as standard for all gas detectors. The case history presented documents the clear identification of formation fluid contacts with higher accuracy than standard light gas detectors, the recognition of contaminants within the drilling fluid, and the practicality of operating an advanced gas detection system with minimal operational and logistic footprint. The new gas chromatograph has been run as a complement of an advanced gas detection system, which comprise a series of crucial elements, all crucial to obtaining high quality, repeatable gas data. The system comprises a constant volume gas extractor, a mud heating system, a sample flow control system, a high-resolution chromatograph for the light fraction of hydrocarbon gases, in parallel with the heavy gas detector, and an automated gas data quality check system.
- Europe (1.00)
- North America > United States (0.94)
- Geology > Geological Subdiscipline > Geochemistry (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.46)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Drilling > Drilling Measurement, Data Acquisition and Automation > Mud logging / surface measurements (1.00)
- Well Drilling > Drilling Measurement, Data Acquisition and Automation > Logging while drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- (3 more...)
Abstract: In the Oil and Gas industry, real-time mud logging measurements have been used since the early 70's with a wide range of applications. The advancement in mud logging measurements is focused on optimizing drilling operations. To reach this goal the historical data of the correlation wells represents a valuable source of information, allowing decrease the uncertainty associated to well planning and execution that can be maximized under technical and managerial circumstances. This paper reports the experiences of real-time advanced logging information integration from the well in progress with the historical data of the correlation wells and how this allowed taking preventive decisions to optimize the density window range more accurately, to evaluate operational parameters and to use the best technologies according to the modeled best practices, to evaluate trends. All this is in order to issue alerts, recommendations, proposal, and mitigations procedures before and during the drilling operations to allow the decision-makers to reduce the NPT and the possible negative HSE impact. The process involves emerging technologies enabling to collect and interoperate data collected by different operators in a transparent way into a knowledge repository that integrates real-time information and offset correlation wells, to analyze and compare the data to the models, to issue alerts and to provide standardized visualization modules in a collaborative environment allowing the decision-makers to reach their goals. 1.-Introduction Surface and down hole data logged from offset wells have always proven vital to optimize the efficiency and success of the current well being drilled. To solve this problem, which was first observed in a Real Time Operation Center (RTOC), the need arose to make a streamlined and better integrated well analysis that would allow preventive measure to be taken in real time by considering the events from the offset wells, Pore Pressure and Fracture Gradient.
Extracting Caliper Data From LWD Propagation Resistivity Measurements: A Unique Methodology to Optimize Real Time Understanding of Borehole Condition
Whyte, I. (Tullow Oil) | Horkowitz, J. (Schlumberger) | Peternell, A. (Schlumberger) | Dong, C. (Schlumberger) | Zhong, L. (Schlumberger) | Leveque, S. (Schlumberger)
ABSTRACT: Caliper measurements from logging-while-drilling (LWD) propagation resistivity data have significant value in that they provide information on borehole size for better estimates of cement volumes, and contain a wealth of time-lapse information to evaluate changes in borehole size related to the drilling process. These measurements are initially acquired just behind the bit soon after it penetrates new formation, and subsequently on all pipe reciprocations and trips. There is no need for additional non-productive rig time and associated cost in obtaining the required measurements. This LWD caliper is computed from data that can be acquired and transmitted in real-time while pumping, or recorded to memory when the pumps are off. What is new and novel about the methodology and applications presented in this paper is the development of an inversion model and forward modeling database created specifically to solve for borehole diameter (Dh), formation resistivity (Rt) and mud resistivity (Rm) in water-based mud (WBM) systems and large boreholes (up to 40 inches in diameter) without a priori knowledge of the mud resistivity. Furthermore, the results can be quickly and easily validated based on drilling information such as over-pulls related to under-gauge borehole and actual cement volume pumped. Interpretation of the information available from this new LWD caliper processing is valuable for a number of drilling efficiency, well construction and well integrity applications. In situations where wireline logs may not be acquired prior to running casing such as the riser-less top hole section of most all deepwater wells, a caliper measurement made during the trip out of the hole is extremely valuable for evaluating the final borehole condition prior to running casing. A number of these applications were recently utilized by Tullow Oil in an ultra-deepwater exploration well to diagnose wellbore integrity issues, optimize drilling efficiency, and reduce non-productive time.
- Well Drilling > Drilling Operations (1.00)
- 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)