The use of radioactive source porosity measurements is strictly prohibited in Bohai Bay, China. As an alternative, logging-while-drilling nuclear magnetic resonance (LWD-NMR) has been applied.

In one block of the Bohai Bay field, it is a big challenge to identify and quantify hydrocarbon reservoir sections due to little resistivity contrast between reservoirs and water zones. LWD-NMR technology and the azimuthal resistivity tool is able to solve this challenge. The low-gradient LWD-NMR tool not only measured porosity also provide T₂ distributions, which can be used for fluid type characterization. The azimuthal resistivity tool has a deep azimuthal resistivity measurement that can identify nearby bed boundaries, up to 5 m from the borehole, while drilling. This information is available in real-time to the operator for decisions while drilling. The combination of the two measurements is capable of differentiating physical properties of the reservoir and providing information on fluid types. Thus, the operator can easily make decisions to optimize the wellbore placement and perform an accurate petrophysical evaluation of the reservoir.

A pilot hole and a horizontal hole are presented in this paper to show the advantages of LWD-NMR and the azimuthal resistivity respectively. In the pilot hole, the LWD-NMR has been used for fluid typing which can give a clear petrophysical interpretation of the reservoir fluids. Because in this low-resistivity contrast reservoir, it is difficult to differentiate oil zones (10+ Ohmm) and water zones (9- Ohmm) from resistivity data. The light oil, however, shows a much slower NMR T₂ relaxation time than the water. Based on the identification of oil versus water by NMR in the pilot hole, three horizontal wells were successfully drilled in the oil zone. In one of them, LWD-NMR and azimuthal resistivity have been employed simultaneously for optimal wellbore placement by enabling to drill in the best part of the reservoir. The LWD-NMR measurements indicated reliably the presence of hydrocarbons and provided important reservoir properties. The azimuthal resistivity measurements identified the reservoir boundaries and the distance to them.

Under complex reservoir conditions as encountered in Bohai Bay, azimuthal resistivity and LWD NMR prove to be an accurate and robust source-less measurement combination. LWD NMR can effectively replace the traditional density-neutron source measurements for porosity. More importantly, the combination with azimuthal resistivity provides the operator with additional critical information for optimal wellbore placement and strengthening the confidence in petrophysical interpretation results.

The coal-seam gas (CSG) industry has long been considered as a high volume, low cost market. As the industry has matured, the selective application of high-tier technologies has realized a step change in performance and real-time formation evaluation results. We investigated whether a high-tier LWD multi-function service could provide a suite of quantitative real-time measurements in several deviated wells. The key objective was to reduce the amount of non-productive rig time spent waiting for memory data in order to confirm the completion design. Significant savings in rig time could be realised if reliable, high-quality real-time data enabled the early identification of coal seams and permeable aquifers such that the swellable packer and slotted liner completion design could be completed without the need for final memory logs.

The area of interest is characterized by thin Jurassic coal seams rather than thick Permian seams. It was critical to accurately identify thin coal beds in real-time whilst maintaining a high rate of penetration (ROP). Low-resolution data would result in poor completion design, underestimation of net coal reserves, and sub-optimal static models. Measuring coal thickness and properties can be difficult due to the fundamental differences between the formation evaluation measurements and their relative axial resolutions. The presence of thin coals can further complicate the interpretation. Another challenge was to optimize the real-time data transmission to prevent any limitation on the key directional drilling data parameters.

Conventional LWD logs (gamma ray, nuclear, and resistivity measurements) provide formation evaluation information while drilling. The selection of a rotary steerable system (RSS) was critical as it ensured directional control and avoided any sliding intervals over key aquifers and coal zones, thereby ensuring optimal LWD acquisition. Advanced formation evaluation options of the LWD data also included using dual-pass resistivity inversions for Rt/Rxo to determine the invasion profile in a permeable aquifer zone above the main coal-producing reservoir. Having this information in real-time was critical in guiding well-specific competition decisions. Induction and laterolog-type resistivity tools were run on one well to quantify differences in the measurements and to determine the best resistivity acquisition tool for CSG wells drilled with saline muds in freshwater formations.

The results showed that high-tier LWD technologies provide multiple benefits in CSG wells. The project was executed with all directional and logging objectives achieved. Quantitative real-time data was critical for completion decisions including ECP placement together with swellable packer and slotted liner designs. This resulted in significant cost savings which are important to major CSG developments operating within a low-cost operating model. LWD memory data provided a rich suite of additional measurements to complement the real-time data. Memory data was used for advanced reservoir analysis with industry-unique measurements.

Pressure analysis is concerned with the study of systematic variations of reservoir pore pressure with depth. The most common interpretation for pressure analysis is pressure-depth plot analysis, but other techniques that magnify understated pressure differences are also available. The measurement of formation pressure is of immense value in quantitative evaluation and prospect risk. Once the pressure data has been acquired, we need to understand how to interpret the data received because reservoir pressure data has numerous applications and misinterpreting it could make the results misleading. At equilibrium state (i.e. there are no net forces and no acceleration), a fluid in the system is called hydrostatic equilibrium. Hydrostatic pressure increases with depth measured from the surface due to the increasing weight of fluid exerting downward force from above. The traditional pressure evaluation is usually done in conventional unit such as psi, kPa, psi/feet, psi/m, kPa/m, ppg. The current work will introduce the concepts and definitions of formation pressure evaluation using Pressure Index (PI) with the unit g/cc. For better understanding of the application of PI, some reservoir studies are also discussed in this paper.

Accurate formation evaluation relies critically, among other inputs, on the correct true formation resistivity (Rt). The common practice in the industry is to use the deep resistivity log as Rt. A single resistivity curve from a deep resistivity measurement often does not represent Rt due to the shoulder bed effect, polarization at boundaries, and many other effects. This is especially true in high angle and horizontal wells. The main objective of the paper is to demonstrate that advanced resistivity modeling workflows for both wireline and logging while drilling (LWD) help in determining Rt by removing or minimizing the impact of all different effects and improving the formation evaluation in vertical and horizontal wells.

Extensive work and computational advances have provided the oil and gas industry with codes to model resistivity tools in a wide variety of formations/conditions. The workflow used is a model-compare-update approach and provides an interface where a layered earth model (layer geometry and property) can be constructed. If available, image logs are used to provide dip information for each layer. After several iterations, and if an agreement between the forward model and measured logs has been achieved (called the "reconstruction check"), this will be a confirmation of the structural model and assigned layer properties. Reconstruction of actual data to modeled data is the confidence indicator. The model changes or iterations can be done manually or automatically. The practical process is usually a combination of both.

As a result, the resistivity logs free of shoulder bed, polarization and other effects are extracted as squared logs for each layer and are used to improve the interpretation methodology and minimize the associated uncertainties to reservoir evaluation. The workflow and benefits of advanced resistivity modeling for improving formation evaluation in vertical and especially high angle and horizontal wells will be discussed. Several field log examples will be used to demonstrate the capabilities of the proposed workflow to enhance formation evaluation in vertical and horizontal wells. Conclusions fromthe work with suggestions/recommendations for the way forward will be presented.

Advanced resistivity modeling when used by the petrophysicists can have many advantages, especially in complex situations. We propose workflows and case studies which demonstrate the value of such advanced modeling in enhancing vertical and horizontal well formation evaluation.

ADNOC's limestone reservoirs suffer from the phenomena of injection water traveling preferentially at the top of the reservoir placing injection water above oil held there by capillary forces. Horizontal wells placed below areas of water override, cause the water above to slump unpredictably, increasing water cut and eventually killing the horizontal. Ultra Deep Directional Electromagnetic (EM) Logging While Drilling (LWD) tools provide the measurements to identify and map these water zones, improving reservoir management and design optimal well placement.

1D & 2D EM inversion modeling was conducted on two of ADNOC's largest oil producing reservoirs to evaluate the ability of an Ultra Deep Directional EM LWD Resistivity tool to identify water slumping in the presence of formation bed resistivity contrasts and predict depths of reliable detection (DOD) under various well trajectory scenarios. The inversion was run using depth of inversions up to 150 ft, the maximum expected vertical distance of tool to injection water. Modeling provided an optimized tool configuration (frequency, transmitter-receiver spacing's) to meet objectives. The inversion results further provided guidance for Geosteering, Geomapping and Geostopping decisions.

The inversion results in these reservoirs indicated that the Ultra Deep resistivity tool has a DOD of 50-150 ft to pick reservoir tops and water slumping or non-uniform waterfront boundaries. The real-time inversion will optimize landing and drilling long horizontal section to increase net pay for production and even through sub-seismic faults, measuring changes in the reservoir fluid distribution, reduce drilling risk and exceed well production life. This information will aid in updating static model with water flood areas, reservoir tops, faults and structure, designing better infill well spacing and trajectories within bypass oil regions, designing proactive and not reactive smart well completions to delay or reduce water production and ultimately extended plateau and improve ultimate recovery factor. Furthermore, it will aid resistivity mapping of underlying or overlying reservoirs for future development plans.

The encouraging results of this study confirmed to move forward with a field trial in these challenging reservoirs for better reservoir and fluid characterization and its management.

This paper present the successful deployment of the ultra-deep EM tool in a mature carbonate reservoirs to reduce the uncertainty associated with fluid movement for horizontal/ MRC well-placement optimization and enable precise geosteering to maintain distance from fluid boundaries and mapping of nearby reservoirs for future reservoir development. In addition, the EM tool can facilitate to optimise lower completion design liner (blank pipe length, PPL, ICD and swellable packer depth).

The high heterogeneity of reservoir qualities increase uncertainty in fluid distribution and make drilling long horizontal, oil producer wells in offshore mature giant carbonate fields very challenging. The usual plan is to drill a pilot hole crossing the reservoir sections, evaluate log saturation, and then re-optimize horizontal sections accordingly. To study the possibility of eliminating pilot holes, an ultra-deep electromagnetic (EM) tool was deployed. The first objective was to detect reservoir boundaries and predict resistivity of the target before penetrating it (Geostopping). The second objective was to optimize the horizontal drain (Geosteering), and map resistivity of adjacent reservoirs for well completion and future well optimisation (Geomapping).

Pre-well inversion modeling was conducted to optimize the spacing and firing frequency selection in order to facilitate early real-time geosteering and geostopping decisions. The plan was to run the ultra-deep resistivity tool in conjunction with shallow propagation resistivity and density-neutron porosity while drilling the 8½ in landing section. The objective was to be able to detect the lithology boundary early and predict the resistivity of the reservoir before penetrating, facilitating geostopping decisions. This would allow optimization of the horizontal section to geosteer the well in an oil-saturated layer 4-6 feet from top boundary while geomapping the surrounding reservoirs’ resistivity.

The EM tool delivered accurate mapping of thin reservoir layers while drilling the 8½ in section, as well as enhanced mapping of low resistivity zones up to 85 feet true vertical thickness in a challenging low-resistivity environment. Comparison to recorded open-hole logs for validation showed good results, enabling identification of the optimal geostopping point in the 8½ in. section.

The EM tool is able to save up to five rig days in the future by eliminating pilot holes. The 6 inch horizontal section was successfully geosteered and placed 4-6 feet from top boundary. The EM tool was able to map reservoir resistivity 30 feet TVD below the wellbore and the completion design was designed accordingly. Additionally, the EM inversion for the nearby reservoirs helped to modify the plans for nearby future wells.

A 20" gasoil pipeline was to be constructed from Sokhna Port to a Terminal at Al-Sadat area on the Suez Hurghada High Way, Arab Republic of Egypt.

The 20" pipeline is a 34 Km long pipeline. The 20" pipeline runs parallel to and in close proximity to Over Head Transmission Lines.

The location of steel pipelines in the vicinity of AC power transmission facilities has resulted in mutual electrical interference problems that can produce damaging effects on both utilities and an electrical hazard to pipeline personnel. The pervasive use of the utility corridor concept necessitates that the electrical interference aspects be clearly defined and guidelines to minimize the harmful effects be incorporated into pipeline and powerline specifications, designs, and operating procedures.

There are three modes of AC interference that can cause damage to pipeline systems and present an electrical shock hazard to pipeline personnel, namely; inductive coupling, resistive (conductive) coupling and capacitive (electrostatic) coupling.

This paper highlights the results of the AC interference study, its effects on the pipeline and the operators during the steady state and during fault current conditions. The paper also highlights the results before and after the AC mitigation measures were implemented.

When drilling in mature reservoirs, conventional formation evaluation is not enough. Characterizing these formations properly becomes essential in ensuring longer and sustainable oil producing boreholes. Understanding the geological complexities, permeability drivers and pressure potential is important since they control fluid flow. This work presents the first ever case study from the Abu Dhabi Carbonates where an innovative multi-measurement borehole imager was deployed, providing a comprehensive and integrated formation evaluation not used before in the industry.

A campaign of five extended reach wells was planned in one field offshore of Abu Dhabi. A 15-ft long borehole imager was added to the drilling bottom-hole assembly (BHA) to acquire apparent resistivity and ultrasonic images simultaneously to characterize the often not-observed geological features that control reservoir properties. These complementing images helped in characterizing vug distributions, bioturbation, faults and dissolution seams in addition to the bed boundaries. Around 13,000ft of lateral was logged while drilling, using this data in real time in oil-based mud to target the most permeable and thinnest layers for the first time in the middle east.

Core analysis had defined the 2ft thick most permeable layer of the reservoir where the lateral needed to be exposed for better production. Multi bed boundary detection for waterfront identification was integrated with mobility pretests points along with surface mud gas fluid sampling for Gas Oil Ratio (GOR) determination and the innovative dual imager. For the first time, acquiring a high resolution apparent resistivity image in real time in OBM, made the restriction of placing the lateral in a thin layer possible. Findings redefined the understanding of the geology and the drivers behind the fluid flow within this reservoir. With the new high definition ultrasonic image, vugs that tend to control the permeability in many facies were discovered. This led to the computation of a vug density curve derived from the images which characterized the key-intervals. Qualitative trends were validated with mobility estimated from independent LWD measurement, providing much-needed confidence in the new imaging technology. Completion was re-designed based on the new brought-in information. Sections were isolated based on the high-water saturation zones mapped with the multi bed boundary detection technology and higher gas oil ratio from surface fluid sampling. Completion was then optimized around high vug density/ mobility intervals.

This first-ever case study provides a plethora of new information for model update whether it be the geology or the reservoir model that was hitherto unavailable for some reservoirs where development wells were drilled with OBM. For challenging wells planned in highly constrained environments from structure, petrophysics and reservoir maturity aspects, this new technology cleverly combined with others, opened the door to boost production from otherwise, a highly matured reservoir.

The strong domestic need for oil in China requires further exploration in unconventional reservoirs, such as volcanic and shale oil reservoirs. Sweet zone identification is one of the most critical missions in formation evaluation. The complex mineralogy and low porosity in unconventional reservoirs result in little variations of resistivities from oil zones to water zones. The uncertainties in fluid typing lower the efficiency in finding the sweet zone.

In conventional reservoirs, nuclear magnetic resonance (NMR) logging based on cutoff analysis is the optimum choice for evaluating the porosity and pore geometry of hydrocarbon bearing reservoirs. However, the routine one-dimensional T2 measurement may not be sufficient for the formation evaluation in unconventional reservoirs, because of the overlap of signals of various fluids in the T2 space. This paper shows a new generation NMR tool with advanced measurements of continuous two-dimensional T1-T2. The T1-T2 measurements enable quantification of different fluids in the pores. Fluid typing is supported by the integration of other wireline logs, such as nuclear spectroscopy and dielectric dispersion.

Case studies are presented from volcanic and shale oil reservoirs in the Xinjiang Oilfield of PetroChina. In the volcanic reservoir case, a modern methodology based on the concept of 2D analytics for extracting signals from two-dimensional NMR T1-T2 measurements is proposed. An integrated workflow derived from wireline borehole image, spectroscopy, dielectric and NMR T1-T2 gives an insight into the fluid composition in the pore system. Besides accurate measurements of lithology independent porosity and pore geometry from NMR, clay bound water volume and total water volume derived from cluster volumetric analysis of NMR T1-T2 match well with those from spectroscopy and dielectric tools. It lowers the uncertainties of fluid typing in the volcanic reservoir where resistivities fail to differentiate water zones and oil zones. In the shale oil case, the reservoir producibility index (RPI) which takes the oil volume as a positive reservoir quality (RQ) index, and kerogen and bound hydrocarbon as negative RQ indexes is illustrated. It proves to be robust in sweet zone identification.

This paper discusses a novel application of a new generation NMR T1-T2 logging method in unconventional reservoirs, which helps the operator ascertain the potential of the reservoirs. The oil zones identified by the new method have promising oil productions. The workflow can also be applied to other unconventional plays in China.

The last marine cycle of Dubai Lower-Cretaceous has left reefal carbonate deposits on paleo-highs from deep basement faults. Those shores face deposits at the edge of the former Bab basin and developed very good reservoir but had a prolonged emersion prior to the deposition of Nahr Umr seal and are often karstified. A successful development relied on high-angle drilling through an unstable seal and advance geosteering within a complex reservoir with a thin oil leg.

A unique drilling approach in the region was designed and executed to deliver these wells safely. Oil- based mud (OBM), casing while drilling (CWD), and steering assembly were deployed to build safely in unstable shale and land at a high angle within the reservoir close to the roof in a relatively slim hydrocarbon column. The reservoir presents a succession of clinoforms. Good porosity and permeability streaks are present with tighter zones. Karsts, often linked with faults, represent a threat to drilling and well completion. The new high-definition reservoir mapping while drilling (RMWD) (6-in reservoir) was introduced to accurately steer within this reservoir.

Simulations of drilling dynamics revealed the best BHA and casing designs. Over seven wells, this method was optimized by using an RSS and executing the 3D trajectory with required build rate and with no compromise on ROP. CWD was used to drill up to 12,481ft MD, which is the deepest in the world for such technology. Without it, inevitable slump down to the water leg would compromise the development of the entire field. The new RMWD technology revealed the reservoir details by mapping over 100 ft thickness of structure and fluid contacts. Subseismic Karsts and the irregular shale-carbonate contacts were precisely delineated. This allowed proactive reactions while drilling and avoided costly sidetracks. Clinoforms were resolved; transition zones and oil water contact depths were mapped. Over the course of seven wells, the information gathered allowed a redefinition of the entire field model from both a geological and reservoir perspective. As result, the original oil in place (OOIP) was recalculated with a renewed field development plan. The technical execution enabled the production of dry oil wells while steering as high as possible within the most permeable layers at a high rate, mitigating karst risk. The introduction of successful CWD eliminated the need to drill the 8^-in section. Four days were saved during the well construction process, and drilling risks associated with unstable and reactive shale were greatly reduced. The new RMWD technology in the lateral section potentially saved millions in development strategies and completion plans by mapping the complete oil column, transition, and water zones while providing safe geosteering away from karstic shales.