A new acoustic tool has been developed to measure formation acoustic properties through casing. This measurement is important for oil and gas production in mature fields, and for wells that are cased without logging due to borehole stability issues. Conventional acoustic logging through casing in poorly bonded boreholes has been a difficult task due to the presence of overwhelming casing waves that mask the formation acoustic signal. To overcome this difficulty, we developed an acoustic tool using dual-source transmitters and the processing technique for the data acquired by the tool. This paper elaborates the operating principle of the new dual-source technology and demonstrates its application to casedhole acoustic logging. By using the dual-source design, the overwhelming casing waves from the poorly bonded casing are largely suppressed. On the basis of the casing-wave suppression and the condition that the formation is acoustically slower than casing, the formation acoustic-wave amplitude is significantly enhanced in the dual-source data-acquisition process. Subsequent processing of the data reliably obtains the acoustic velocity of the formation. The new tool has been tested in many cased wells with proven performance for various cement-bond conditions. The success of this technology makes casedhole acoustic logging an effective operation that can be routinely used to obtain reliable formation information through casing for slow to moderately fast formations.
Sheng, Xiaofei (Tianjin University) | Shen, Jianguo (Tianjin University) | Shen, Yongjin (Beijing Huahui Shengshi Energy Technology) | Zhu, Liufang (Logging Company of Shengli Petroleum Engineering Co.) | Zang, Defu (Logging Company of Shengli Petroleum Engineering Co.)
Transient electromagnetic (TEM) logging is a promising noncontact method for through-casing formation conductivity measurements. We studied the through-casing TEM logging method based on the processing of TEM logging data measured in a production well. Similar to Doll’s work in borehole induction logging, we presented the expressions of the ‘useful signal’ and the ‘useless signal’ in casedhole logging based on which, the methods of removing the ‘useless signal’ and obtaining the formation conductivity curve are introduced. We analyzed the influence of the casing on the TEM signals, described the characteristics of TEM response signals, and obtained the ‘useful signal’ carrying formation conductivity data. Casedhole formation conductivity curves, which are subsequently compared with the known openhole conductivity log, are obtained by dealing with the ‘useful signal’. We identified the characteristics of casedhole formation conductivity curves, and some problems that need to be considered in their practical application. Due to the influence of the casing, the radial detection depth of the TEM logging tool in a cased hole is small, so the detection result is mainly the equivalent conductivity of the cement ring and formation near the outer casing wall. Although the casedhole conductivity curves are in good agreement with openhole logging results in regular formations, due to the influence of the casing and the changes in the physical environment in the well, complete consistency is unrealistic for these two kinds of curves in all well intervals. Therefore, a thorough analysis is required before practical application. Moreover, the effects of well temperature and casing deformation must be corrected for accordingly.
Borehole measurements are often subject to uncertainty resulting from the effects of mud-filtrate invasion. Accurate interpretation of these measurements relies on properly understanding and incorporating mud-filtrate invasion effects in the calculation of petrophysical properties. Although attempts to experimentally investigate mud-filtrate invasion and mudcake deposition have been numerous, the majority of published laboratory data are from experiments performed using linear rather than radial geometry, homogeneous rock properties, and water-based (WBM) rather than oil- or synthetic oil-based drilling mud (OBM or SOBM).
We introduce a new experimental method to accurately reproduce conditions in the borehole and near-wellbore region during, and shortly after the drilling process, when the majority of wellbore measurements are acquired. Rather than using a linear-flow apparatus, the experiments are performed using cylindrical rock cores with a hole drilled axially through the center. Radial mud-filtrate invasion takes place while injecting pressurized drilling mud into the hole at the center of the core while the outside of the core is maintained at a lower pressure. During the experiments, the core sample is rapidly and repeatedly scanned using high-resolution X-ray microcomputed tomography (micro-CT), allowing for visualization and quantification of the time-space distribution of mud filtrate and mudcake thickness. Because of the size of the core sample, the developed experimental method allows for accurate evaluation of the influence of various rock properties, such as the presence of spatial heterogeneity and fluid properties, including WBM versus OBM, on the processes of mud-filtrate invasion and mudcake deposition. Results indicate that our experimental procedure reliably captures the interplay between the spatial distributions of fluid properties and rock heterogeneities during the process of mud-filtrate invasion.
A well was drilled into a prospective new unconventional mudstone play offshore Norway. Two of five coring runs were successful while the rest yielded little to no core recovery. Investigations attributed the poor recovery to sub-optimal coring practices, equipment failure and operational errors. Recently, the accompanying petrophysical logs and seismic data were revisited, and upon detailed investigation several unusual responses were observed to correspond with intervals of poor core recovery. Subsequent investigation of the core itself substantiated that the coring issues largely had natural causes. This understanding is being applied to two imminent coring operations and has driven selection of drilling, coring and wireline technology and procedures, in addition to informing casing design.
Wireline nuclear magnetic resonance (NMR) and cross dipole acoustic data, logging whilst drilling (LWD) density (including azimuthal images), neutron porosity and resistivity was acquired over the interval of interest for standard formation evaluation purposes. This interpretation was conducted immediately after the initial drilling and showed the formation to be a series of highly porous oil bearing mudstones. However, no in depth advanced interpretation was conducted at the time. Recently, advanced analysis including high resolution log enhancement, NMR 2D porosity and saturation analysis, acoustic azimuthal anisotropy, near wellbore imaging, fracture interpretation, and borehole image interpretation were performed on the log data, and new and improved 3D seismic data was interpreted. When interpreted in detail it could be observed that unusual responses in the logs showed a close correspondence to the intervals of poor core recovery. In particular, high azimuthal anisotropy was observed, and when this was compared to the near wellbore reflection image a significant planar reflecting feature was identified which is determined to be a fault. Indications of this feature was subsequently found in seismic data. When then compared to the azimuthal density image after resolution enhancement was applied, although the image is still of too low resolution to directly image the fault, disturbed bedding was observed which is commonly associated with faulted intervals. Several core fragments proved to have extensive small-scale fracturing not noticed previously, and slickenlines were found along several larger fractures previously presumed to be drilling induced.
The investigations of the log data revealed that a previously unknown sub-seismic fault was present right below the depth where coring problems were encountered. The detailed interpretation was able to determine the precise location of the fault and its extent in the formation. Knowledge of this subsequently explained the coring problems encountered and helps to optimise imminent coring in the same formation. Lessons learned and the methodology likely also applies to similar formations.
In this paper we discuss coring issues encountered in a new and unconventional play offshore, present new data and interpretation that sheds light on them and describe the methodology of the detailed integrated interpretation that uncovered the previously unknown root cause. We then discuss how these findings can be (and are) used to optimise both drilling, coring, and logging operations in future wells.
Directional drilling for hydrocarbon exploration has been challenged to become more cost-effective and consistent with fast-growing drilling operations for both offshore and onshore production areas. Autonomous directional drilling provides a solution to these challenges by providing repeatable drilling decisions for accurate well placement, improved borehole quality, and flexibility to adapt smoothly to new technologies for drilling tools and sensors. This work proposes a model predictive control (MPC)-based approach for trajectory tracking in autonomous drilling. Given a well plan, bottomhole assembly (BHA) configuration, and operational drilling parameters, the optimal control problem is formulated to determine steering commands (i.e., tool face and steering ratio) necessary to achieve drilling objectives while satisfying operational constraints. The proposed control method was recently tested and validated during multiple field trials in various drilling basins on two-and three-dimensional (2D and 3D) well plans for both rotary steerable systems (RSS) and mud motors. Multiple curve sections were drilled successfully with automated steering decisions, generating smooth wellbores and maintaining proximity with the given well plan.
Ahmadian, Mohsen (Advanced Energy Consortium, Bureau of Economic Geology, The University of Texas at Austin) | LaBrecque, Douglas (Multi-Phase Technologies, LLC) | Liu, Qing Huo (Duke University) | Kleinhammes, Alfred (The University of North Carolina) | Doyle, Patrick (The University of North Carolina) | Fang, Yuan (Duke University) | Jeffrey G, Paine (The University of Texas at Austin) | Lucie, Costard (The University of Texas at Austin)
Characterizing hydraulically induced fractures—height, length, orientation, and shape—is key to understanding reservoir performance. Our previous work has focused on the comparison of the state-of-the-art geophysical techniques currently used in hydraulic fracture imaging (microseismicity, tracer, tiltmeter, and distributed acoustic and temperature sensors) to perform a comprehensive set of electromagnetically active proppant (EAP)–assisted tomography methods (
Costin, Simona (Imperial Oil) | Smith, Richard (Imperial Oil) | Yuan, Yanguang (Bitcan Geoscience and Engineering) | Andjelkovic, Dragan (Schlumberger Canada) | Garcia Rosas, Gabriel (Schlumberger Canada)
Open-hole mini-frac tests are seldom performed in the Athabasca and Cold Lake oil sands due to the complexity of operations. In this paper we present the results of open-hole injections tests performed in Cold Lake, Alberta (AB), Canada. The objective of the injection tests was to assess the in-situ stress condition in the Cretaceous Colorado Group. The injection tests results combined with the run of formation image logs (FMI) before and after the injection have enabled not only the determination of the in-situ minimum stress in the rock, but also the full 3-D stress tensor, along with the orientation and inclination of the hydraulic fracture. The tests were performed in IOL 102/08-02-066-03W4 (N10 Passive Seimic Well, 'PSW'). The injection tests have revealed that the vertical stress in the area is the in-situ minimum stress, consistent with previous measurements. The hydraulically-induced fracture has sub-horizontal to moderate dip angle, mostly owing to the preexisting fabric of the rock, and peaks in the general NE-SW direction. Numerical modeling of the in-situ stresses has shown that the values of the vertical and the minimum horizontal stresses are close, with the vertical stress consistently being smaller than the minimum horizontal stress in all tested zones.
A new cased-hole porosity measurement has been developed for a four-detector pulsed-neutron logging tool. The measurement is based on a capture count rate ratio from two different detectors. To determine an accurate porosity, the ratio is characterized in the laboratory in order to establish a ratio-to-porosity transform. To account for varying measurement conditions in the field, environmental corrections, based on laboratory studies and computer simulation, are applied. As an alternative to environmental corrections, the capture ratio can also be actively compensated for the environment by using the results of a dual-exponential fit to the capture time decay spectrum. In particular, we can compensate for the borehole fluid salinity by using the borehole component of the dual-exponential fit, and we can compensate for the effective density of the borehole environment by using an inelastic ratio derived from the capture subtracted burst yields. The final porosity measurement has been shown to provide accurate results in the field through a comparison with data from open-hole logs.
Galford, James (Halliburton) | Ortiz, Ricardo (Halliburton) | Neely, Jeffrey (Halliburton) | Heaton, Jennifer (Halliburton) | Vehra, Imran (Halliburton) | Wu, Junchao (Halliburton) | Leung, Matthew (Halliburton) | Chandrashekar, Natesh (Halliburton)
Today’s fast-paced development of petroleum resources depends on an efficient and accurate evaluation of both clastic and unconventional reservoirs. A new high-performance, slim logging-while-drilling (LWD) natural gamma ray spectroscopy tool has been developed to assist real-time petrophysical evaluations of net-to-gross for conventional reservoirs and to identify "sweet spots" for completion for unconventional reservoirs. Additionally, its azimuthal sensitivity can help position the well in lateral operations.
This new tool provides wireline quality formation thorium (Th), uranium (U), and potassium (K) elemental concentrations in real time that can quantify clay content, identify clay minerals, and estimate total organic content. Further, real-time processing provides a color display derived from a Briggs color cube rendition of relative elemental contributions that can be correlated with stratigraphic features in the field. This first-of-its-kind, real-time feature is output at a high sampling rate for the full azimuth of the borehole and should be a useful aid in geosteering applications where the goal is to maintain the borehole within a target formation or to follow a known stratigraphic feature.
Calibration and characterization of the tool were performed using newly developed Monte Carlo modeling techniques superior to previously used laboratory techniques while maintaining direct links to industry standards at the API Gamma Ray Calibration and K-U-Th Logging Calibration Facilities at the University of Houston. These techniques were developed because the borehole at the API Gamma Ray Calibration Facility cannot accept the 5.25-in. collar diameter, and the potassium formation at the API K-U-Th Logging Calibration Facility is not reliable. The instrument is fully characterized for operations in barite-, hematite-, or formate-weighted water-based mud systems as well as barite- or hematite-weighted oil-based muds. Further, corrections for borehole potassium can be applied in real time.
A novel mechanical design enables the sensor to operate at temperature up to 329°F and borehole pressure up to 25,000 psi while minimizing the attenuation of formation gamma rays entering the detector and maintaining good azimuthal sensitivity. The tool uses a robust, constrained, weighted least-squares (WLS) analysis to derive elemental concentrations from measured pulse-height gamma ray spectra. Proprietary spectral processing algorithms regulate the detector gain without the use of an additional radioactive reference source and compensate for variations of the detector’s energy resolution caused by operating conditions within the borehole that change over time. A general description of the tool together with its operational specifications, details of the computer models used to calibrate and characterize its responses, and example logs from early field trials are within this paper.
Joshi, Deep (Colorado School of Mines) | Eustes, Alfred (Colorado School of Mines) | Rostami, Jamal (Colorado School of Mines) | Gottschalk, Colby (Colorado School of Mines) | Dreyer, Christopher (Colorado School of Mines) | Liu, Wenpeng (Colorado School of Mines) | Zody, Zachary (Colorado School of Mines) | Bottini, Claire (Colorado School of Mines)
Water is considered the ‘oil of space’ with applications ranging from fuel production to colony consumption. Recent findings suggested the presence of water-ice in the Permanently shadowed craters on Lunar poles. This water present on the Moon and other planetary bodies can significantly bring down the cost of space exploration, fueling the colonization of the solar system. With low-resolution orbital data available, the next step is to drill and analyze samples from the Moon.
An extensive review of drilling systems designed by NASA was conducted focusing on the effect of different planetary environments on the drill design. Inspired by this and the drilling systems developed in the petroleum industry, an auger based rotary drilling rig was designed and fabricated with an extensive high-frequency data acquisition system, measuring all essential drilling parameters. Several analog rocks were cast with regolith simulant grout to replicate different subsurface geotechnical properties in the Lunar polar craters. The drill was tested on samples with different geotechnical properties to account for the varying properties expected in the Lunar poles.
Application of the drilling engineering concepts has resulted in the development of a robust drilling system capable of replicating drilling process for different planetary environments like the Moon and Mars. Using the data acquisition system on the rig, an advanced machine learning algorithm capable of processing and analyzing the real-time high-frequency drilling data to estimate a sample's geotechnical properties and water content was created. The evolving algorithm was developed based on initial drilling tests on homogenous and heterogeneous analogs. It was tested on samples with varying heterogeneity to estimate the geotechnical properties and the water content accurately. With some modifications, this algorithm can be applied in the Lunar and Martian missions to estimate the geotechnical properties in real-time, without the need to analyze the subsurface samples on the surface. This can result in a cost-effective exploration of water-ice resources on the Moon and Mars, kickstarting the space resources industry and the human colonization on those planetary bodies. The expertise of the drilling engineers in designing and executing wells in extreme terrestrial environments can help create significantly effective drilling systems for extraterrestrial environments.
This work details the design considerations to drill on the Moon and other planetary bodies focusing specifically on the application of drilling data to evaluate geotechnical properties and water content at Lunar polar conditions. The techniques developed here might pay a vital role in understanding the extent and composition of water-ice on the Moon, leading to efficient colonization of the solar system.