TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractReservoir navigation with LWD resistivity has traditionally relied on matching real time measurements with ideal logs. Reservoir navigation engineers initially build one or more resistivity models including all expected resistivity boundaries such as oil-water contact, reservoir to cap rock interface, faults and unconformities. Then, during drilling, they direct the well and update the earth model by matching actual measurements with forward response model data.Because common LWD resistivity sensors cannot differentiate between an oil-water contact approaching from below and a shale lens approaching from above or from the side, the reservoir navigation engineer fills in the missing information through expertise and local knowledge. In case of complex geology however, such as reservoirs with tilted or rotated fault blocks, multiple fluid contact levels, cross-stratification and shale intrusions, navigation becomes much more challenging and the risk of getting geologically lost is high. In recent years imaging LWD tools were introduced to help reduce the azimuthal uncertainty but they were limited to a few inches in lateral investigation.A new azimuthally sensitive propagation resistivity tool was recently tested for reservoir navigation and formation imaging in some of the more complex reservoirs of the North Sea. In cases where standard omni directional tool responses would lead to ambiguous interpretations, the azimuthally sensitive tool provided the basis for clear geosteering advice. A new imaging algorithm helped visualize approaching beds much like modern imaging devices, but with a depth of investigation reaching several feet into the formation. At fault crossings, the azimuthally sensitive signal helped recognize the relative movement of the formations on either side of the fault. In other instances where the well was run immediately below the cap rock, deep looking azimuthal propagation anticipated the intersection by several hundred feet. Also, analysis of the detailed deep electrical images brought a more complete understanding of the subsurface.
fax 01-972-952-9435. AbstractWe illustrate the use of a new technology for navigating and characterizing various types of oil reservoirs. Real-time images from Azimuthal Propagation Resistivity measurements provide a "map" of the resistivity patterns up to several meters around the wellbore. In addition, recently developed processing and quantitative interpretation techniques help guide the placement of the well and provide a new perspective of the formation.When navigating in gas drive reservoirs, the azimuthal resistivity measurement is used to maintain the wellbore at a prescribed distance above the oil-water contact. With its exponential sensitivity to distance, the measurement is able to detect even small changes in the distance to the oil-water interface. In a few instances, the azimuthal information provided by the real-time deep resistivity images indicates probable coning due to offset well production.Similar principles are applied in high angle drilling of water drive reservoirs. The deep azimuthal information allows the drilling engineer to maintain the wellbore at a prescribed distance immediately below a shale roof. The deep resistivity image from the azimuthal resistivity measurement also makes it easy to distinguish the roof from the occasional approaching shale lens.Whereas shallower reading LWD image logs (e.g. Gamma Ray and Density) only indicate a geological feature proximal to wellbore, the deep reading azimuthal resistivity measurement can provide geologic structure information at the reservoir scale. Visual displays show the subsurface surrounding the wellbore; quantitative algorithms accurately compute the distance, direction, and apparent dip for reservoir related geological events. A new conductivity unit named "Transverse Siemens" is proposed to help quantify the new azimuthal propagation measurement.
The Grane field causes significant challenges with respect to reservoir drainage and wellbore placement. The true resistivity profiles from offset wells are reflecting an irregular oil water transition zone in the field, likely to be caused by subtle facies variations and/or local variations in the oil water contact (OWC). In addition, horizontal wells penetrated many shales.Baker Hughes INTEQ has in collaboration with Hydro developed an extra deep resistivity service called DeepTrak™ to navigate at a distance of up to 12 meters from a resistivity contrast boundary. This service has been used in several wells.The tools as well as the surface software components provided full service capability and were used successfully to geosteer along the OWC at the required distance. In addition, the DeepTrak service was capable of detecting shale injectites, thus giving valuable insight for reservoir characterization and geological model update.By use of field data, it is demonstrated how the DeepTrak service can be used for accurate wellbore placement.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSince the advent of steerable motors in the mid 80's, the drilling of complex horizontal 3D wells has become a standard in development drilling. To further extend the envelope and optimally position the wellbore to improve drilling efficiency and optimize production more sophisticated systems were required. Now two decades on, the industry has developed intelligent Rotary Steerable Systems (RSS) and sophisticated Logging While Drilling technologies that have both lowered well cost through NPT reduction and given the operator the opportunity to position the well path optimally in the reservoir, based on real time logging data. This environment has placed an increased reliance on Logging-While-Drilling (LWD) measurements. In this paper we will review wells drilled and logged on a North Sea field and how the application of a number of advanced LWD technologies have maximized answers through acquiring full formation evaluation in a single pass. We will discuss the importance of having an integrated LWD system engineered for diverse drilling applications and also designed as a compact, modular system with sensors close to bit with increased flexibility and a wide range of measurements. The realtime aspects of LWD are important in delivering valuable answers. Examples will be illustrated, which demonstrate the value of these technologies in accurate estimating reserves, well positioning, non-productive time (NPT) reduction and drilling hazard mitigation. With such a complex, integrated system, a thorough approach to pre-job planning, realtime follow-up and post-well analysis is a key factor in achieving full formation evaluation data acquisition in parallel with improved drilling performance.
The drilling of horizontal and extended reach wellbores is being revolutionized by rotary steerable systems such as the AutoTrak™ tool. Typically, advanced directional drilling has been performed with steerable mud-motor systems. However, drilling with a steerable mud-motor results in a rough and tortuous wellbore due to the motor's geometry and operational behavior. A rough wellbore may affect the performance of various logging sensors deployed with the system. Different logging sensors are affected differently, and so the ability to compensate for borehole effects varies from sensor to sensor. The result may be a log that suffers in quality. Rotary steerable systems drill smoother and less tortuous wellbores. As a consequence, typical borehole effects visible on various FE logs may not be apparent when drilling with rotary steerable systems. Knowledge of the logging environment in which the data were obtained is important when analyzing the log. It is believed that the introduction of rotary steerable systems will improve the economics of long horizontal and extended reach wells. As a consequence, there will be an increase in the drilling of these types of wells. It is desirable to log these wells while drilling, as the deployment of wireline-operated logging tools will be costly and risky. The real-time logging information can be used for navigating in the reservoir and optimizing the wellbore position. Also, FE-MWD logging sensors are continuously being developed and improved, so the desire to perform the logging operations while drilling will tend to increase. This paper discusses the differences in logging environment as a result of drilling with a rotary steerable system as opposed to a steerable motor system. The paper also discusses the impact of this new logging environment on the results from various FE-MWD logging sensors. Examples of logs recorded in comparable formations with the two drilling systems are included. This may help log analysts in their interpretation of log results, as rotary steerable systems are more commonly used for horizontal and extended reach drilling (ERD).
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