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Wijaya, Aditya Arie (Halliburton) | Aulianagara, Rama (Halliburton) | Guo, Weijun (Halliburton) | Naibaho, Fetty Maria (Pertamina Hulu Sanga-Sanga) | Asriwan, Fransiscus Xaverius (Pertamina Hulu Sanga-Sanga) | Amirudin, Usman (Pertamina Hulu Sanga-Sanga)
ABSTRACT In mature fields, pulsed-neutron logging is commonly used to solve for remaining saturation behind the casing. For years, sigma-based saturation has been used to calculate gas saturation behind casing; however, the high dependency of sigma-to-water salinity of the formation, especially the low dynamic range at porosity near 12 p.u., has proven to be challenging in the low-porosity, gas rock. A new measurement from the third detector from a multi-detector pulsed-neutron tool (MDPNT) is proposed to provide a better estimation of the gas saturation in a low-porosity reservoir. Two sets of independently measured sigma and the third detector were taken in a cased hole well, with a dualtubing system of a long string and short string. For the third-detector measurement, the measurement was based on the ratio of slow capture gate and inelastic gate component from the decay curve created by the long detector. This ratio can be used to detect gas in a tight reservoir with a minimum salinity and lithology effect. This data will then be used to calculate the gas saturation from the third detector, and the result is compared to sigma-based gas saturation. At an interval where the porosity is above 12 p.u., the sigma-based gas saturation and MDPNT-based gas saturation are very much in agreement. However, in a low porosity reservoir near 12 p.u. or below, the sigmabased measurement starts to show its limitation. Meanwhile, the MDPNT-based gas saturation clearly shows the remaining gas saturation where sigma-based measurements failed to detect. The subsequent decision was made based on the log analysis result, and perforation was done at a potential interval based on MDPNT result. The results from the production test confirm the MDPNT-based gas saturation with 700 MSCFD gas production added. This study showcases a new technology to solve a lowporosity gas reservoir issue where a sigma-based measurement underestimate the remaining gas saturation. Using two different measurements in the same well, the results from the MDPNT measurement demonstrated a better result compare to the sigma-based measurement in low-porosity rock.
Abstract Borehole Imaging technology is often key for reservoir characterization and becomes more relevant when images are acquired while drilling to capture reservoir geology and petrophysical property distributions around the borehole. Logging While Drilling (LWD) high-resolution electrical/acoustics images of the borehole can resolve formation layers and heterogeneity down to 5mm (0.2in) scale and can detect response from far smaller features. This allows both, improved operational efficiency and better-informed drilling as well as shortening of the geological interpretation turn-around time from wireline logging time (days after drilling) to semi-real time (drilling time or hours after drilling). LWD high resolution images often suffer from the lack of direct downhole velocity measurements against the sensors. Depth tracking is on surface, referenced to the surface block movement. The imaging sensor acquiring data can be thousands of feet away from this surface reference. Imaging sensors on the bottom-hole assembly (BHA) are located not too far away from the drill bit. They are also subject to complex drilling-time motion such as tool whirling, stick and slip, vibration, mode coupling etc. This can make the downhole sensor movement dis-synchronized with the surface pipe depth increment. The Time-Depth conversion may accordingly get dis-synchronized to generate LWD depth image with missing features and distorted feature-integrity in depth. In severe conditions distorted image impacts real time image feature interpretation and leads to increased interpretation uncertainties. In this paper we investigate two main dissynchronization problems using synthetic data: heave effect and BHA stick and slip effect. Pseudo velocity is computed from the surface measurement due to the lack of downhole sensor velocity direct measurement. In order to minimize heave effect, an advanced band-pass filter is proposed. The filter order is chosen in consistency with the sensor’s pseudo velocity behavior. Other properties of this advanced filter are also presented. In order to minimize the BHA stick and slip effect, pseudo velocity is analyzed as a delayed and minimized representative of the downhole sensor movement. A windowed-thresholding method is proposed to restore the compressed and stretched image features. Dip error analysis is performed by picking bed and fracture surface on the synthetic image data, before and after image distortion correction. The analysis results show a non-negligible effect on the accuracy of the true dip computed if the distortions are left un-corrected. Even in favorable logging conditions, the apparent dip error can contribute up to 50% of the total error. In this case, the image post-processing method proposed in this paper can not only improve the image quality but also reduce image interpretation uncertainties.
Abstract This is a review paper on applying Magnetic Resonance Imaging Logging (MRIL) methods for detecting and quantitatively measuring volumes occupied by brine, gas, and oil. These methods include Differential Spectrum Method (DSM), Enhanced Diffusion Method (EDM), Shift Spectrum Method (SSM) in transverse relaxation time (T2) domain or in spin-echo time domain (i.e., Time Domain Analysis; TDA), Total Porosity Measurement (TPM), and Injecting Contrast Agent Method (ICAM). The principles, data acquisitions, and data processes of these methods and their applications are introduced and discussed. P. 593
Donald, J. Adam (Schlumberger) | Wielemaker, Erik (Schlumberger) | Schlicht, Peter (Schlumberger) | Lei, Ting (Schlumberger) | Mishra, Anoop Kumar (Al Yasat Petroleum Company, ADNOC) | Samantray, Ajay Kumar (Al Yasat Petroleum Company, ADNOC) | Al Mazrouei, Sultan (Al Yasat Petroleum Company, ADNOC) | Thatha, Rajesh (Petromac) | McCormick, Stephen (Petromac)
ABSTRACT An innovative technique orients and centers wireline toolstrings in the wellbore to ensure high-quality data acquisition. The system comprises wheeled carriages and angled guides and takes a holistic approach to wireline tool conveyance, reducing drag while ensuring optimum sensor positioning and orientation for each logging measurement. Correct positioning is achieved through management of the tool center of gravity relative to the wheel axes. Positive toolstring orientation with ultralow-friction wheeled carriages replaces traditional positioning accessories such as bow-spring centralizers and/or powered multiarm calipers. The system improves data quality and enables gravity descents to extreme deviations (up to 80°) that were previously the domain of logging-while drilling, drillpipe, and tractor conveyance. The oriented conveyance system provides sonic centralization, prevents rotation of the formation imager, and reduces stick/slip motion, which is essential for obtaining high-resolution data. Centralization of the array sonic tool is critical for data quality, irrespective of whether the requirement is simply sonic slownesses or involves more complex dipole anisotropy and reflectivity analysis. It is equally important that the logging tool is parallel to the wellbore with no sag or tilt. In deviated wells, it is often difficult to optimize standoffs and bow-spring centralizers to provide centralization while maintaining smooth tool motion for quality data. In addition, powered multiarm calipers introduce additional drag and increase the likelihood and severity of stick/slip. Smooth tool motion is critical when sonic imaging data is acquired to examine fractures and structure in the far field. Centralizing sonic tools by using wheeled carriages remedied these problems and resulted in improved data quality in a recent well with 79° deviation. Examination of the slowness dispersion analysis and single-sensor azimuthal receiver data of the array sonic along with finite-difference modeling of the waveforms verify the effectiveness of the centralization. Excessive stick/slip of wireline toolstrings causes replication of high-resolution subsurface data and small intervals are missed entirely, resulting in a mismatch between actual and recorded depth intervals. The resulting degradation of array sonic measurements and borehole image quality is not recoverable. The wheeled carriages facilitate smooth tool movement, resulting in improved-quality data. Tool rotation, due to the release of cable torque, often results in overlapping images from toolstrings with axially spaced pad sensors in contact with the wellbore wall. The new system locks the tool into a set orientation, preventing rotation. The improvements in data quality combined with efficiency enhancements and the reduction of risk during wireline logging deliver a superior method of conducting operations. Examples are shown for assessment of valid sonic and borehole image results.
Badruzzaman, A. (Chevron Petroleum Technology Co.) | Neuman, C.H. (Chevron Petroleum Technology Co.) | Adeyemo, A.O. (Chevron Nigeria Limited) | Dodman, C.A. (Chevron Nigeria Limited) | Skillin, R.H. (Chevron Western Basins Group) | Zalan, T.A. (Chevron Western Basins Group) | Badruzzaman, T. (Pacific Consultants & Engineers) | Bilodeau, B.J. (Chevron Overseas Petroleum Inc.) | Logan, J.P. (Caltex Pacific Indonesia) | Limon, M.A. (Chevron SouthAmericaBusiness Unit) | Belanger, D.L. (Cabinda Gulf Oil Company) | Featherstone, C.J. (Cabinda Gulf Oil Company) | Nguyen, P.T. (Chevron Petroleum Technology Co.)
Abstract The recent advances in pulsed-neutron technology for oil field applications are discussed. The progress includes applying the technology to a number of formation evaluation and production logging problems, use of Monte Carlo modeling to understand response in complex field-like conditions, and development of interpretation algorithms in non-calibrated conditions. The remaining challenges in current applications and a number of emerging or proposed measurements using the technology are described.