Horizontal drilling is fast becoming an effective economical solution to maximize the asset value for E & P companies. Since established in 2009, TATWEER petroleum is one of those companies that utilize horizontal drilling intensively to improve the production and the recovery factor from tight and fractured carbonate reservoirs within the Bahrain Field. Reservoir complexity and heterogonity create the need for running open-hole logs in most of the horizontal wells within the Bahrain field. Logging is essential for the following: Designing the well completion (Open hole or Slotted liner equipped with external packers), predicting and understanding the well performance, and planning future work-over activities (Water and Gas Shutoff). Normal practice to deploy open hole logging tools into the HZ horizontal section within the Bahrain field was to use drill pipe (Tough Logging Conveyance). Given the typical low productivity of wells, operational costs were of concern. Consequently, TATWEER requested alternative methods to optimize the logging operations in horizontal wells. Of the options offered by Schlumberger, tractoring technology was deemed to be best. The main challenge faced initially was with tractoring in the low uniaxial compressive strength (UCS) of the reservoir formations (UCS=1400-3000 PSI) in Bahrain. Since tractoring is known to be an effective deployment method for hard formations (UCS>5000 PSI), the new OH tractoring technology (UltraTRAC*) was offered by Schlumberger as a solution for this low UCS enviroment. UltraTRAC* was successfully deployed in TATWEER wells, saving 60-70% of the logging time comparing to the normal TLC (Tough Logging Conveyance) operations which represents 5% saving of the total well cost. In this paper, the authors discuss the details of this new logging methodology, logging results, and value obtained from using this technology.

Natural gas is the primary source of energy in Bahrain, and the Khuff reservoir is the main supplier for this gas 4 . The Khuff reservoir, which was discovered in 1948, is composed of four limestone layers (K0, K1, K2, and K3) separated by tight limestone and anhydrite beds that can act as permeability buffers in some areas of the reservoir.In such a mature carbonate gas reservoir as the Khuff, managing and optimizing the performance of wells represents a challenge for the reservoir and production engineers because of the reservoir heterogeneity created by dissolution process which induced good porosity and permeability zones within a lower quality matrix rock; differential depletion, which occurs because reservoir heterogeneity creates a pressure difference between layers; and the commingle production as Khuff wells are completed comingled using either openhole or perforated completion.An integrated workflow applied to Khuff wells helped to understand the well performance and to optimize the workover activities. The process integrates the geological information, openhole data, multirate production logging test data, time-lapse corrosion logs, multilayer transient testing, and nodal analysis and is used to determine the remedial job that is required to achieve the most favorable well performance.The process was applied to one of the Khuff wells that was originally completed as K2 producer and then K1 and K0 were added in double casing using a small gun size because of completion limitations. The well performance after adding K1 and K0 was below expectation, and conclusion was made that the new perforations are not performing as been expected because of insufficient formation penetration. Thus, proposed remedial actions were to reperforate the K0 and K1 intervals using a bigger gun size and then stimulate them. However, before starting this costly operation, the integrated workflow process was used to assess the need for this workover operation. The integrated evaluation showed a different conclusion, which led to different workover plan, thus saving the cost of a more expensive workover operation.

Specifying the perforation intervals and evaluating the productivity of thin-bedded sands and shales is crucial for well completion cost optimization. This requires the accurate identification of hydrocarbon-bearing sands and their contribution to production. Relying only on borehole-imaging tools to select the productive intervals is not suitable in this lithologic type because of the difficulty of permeability quantification. In this paper we present a technique to integrate the detection of hydrocarbon-bearing sands with water saturation information and an estimation of permeability. Hydrocarbon-bearing sands are detected by high-resolution resistivity from borehole-imaging tools combined with water saturation from openhole logs (OHL), and permeability from nuclear magnetic resonance (NMR) or a modular dynamic tester tool. We use the geostatistical concept of indicators to convert the inputs from these tools into binary data (0 and 1) based on the best selected cutoffs for those inputs, where a value of 1 means that location is good to perforate. The results of this integration are compared to the results from the production logging tool that is sensitive to the laminated sand units for evaluating its actual productivity. The best cutoffs to select for those parameters are in good agreement with the production logging tool results. The result is a set of optimized perforation intervals consistent with all the data. In addition to the certainty percent associated with the selection of perforation intervals. Three gas wells producing from the same formation were used to apply this technique. One of the three wells was used to select the best cutoffs. For the other two wells, we used the same cutoffs to select the best perforation intervals and determine the certainty associated with them. The correct selection of the perforation intervals from the two wells was confirmed with the production testing and production logging results. Introduction High-resolution resistivity (SRES) tools are essential to identify the hydrocarbon-bearing layers in thin-bedded formations. However, hydrocarbon-bearing layers are not necessarily productive layers. Recently it was noticed that exploration and production (E&P) companies are relying on the borehole imaging tools to identify the perforation intervals. However, we have noticed from the production logging results performed across these formations that relying only on one tool to select the perforation interval is not the best approach. We saw the need to integrate different tools to assist in selecting the perforation and assessing the uncertainty associated with this selection. The following parameters have great impact in selecting the perforation intervals in thin-bedded gas reservoirs:The high-resolution resistivity to detect the thin sand bedsThe permeability for the productivity of the sand bedsThe water saturation from conventional openhole log interpretation for the hydrocarbon in place quantification. The objective of this study was to select the perforation intervals based on the integration between these three parameters. Thus, it was important to know how we can integrate these independent parameters with completely different dimensions to select the correct perforation intervals. Since our objective was to select specific intervals for perforation, we used the concept of an indicator1 to get a vertical indicator map for each parameter. An indicator of 1 means the location is a good candidate for perforation, and 0 means it is not a good candidate. The indicator map of each parameter depends on the threshold or the cutoff values selected for each parameter that will be selected based on the production-logging tool for the key well.

Conventional production logs; spinner, density, capacitance, temperature, and pressure are routinely used in the Gulf of Suez (GOS) wells for reservoir monitoring and diagnosing production problems. These logs can adequately determine flow profile of fluids inside vertical or moderately deviated holes. However, these were found unsuitable for more complex problems including the following,–Identification of water entries or exits in horizontal wells.–Water flow behind casing in cement channels or behind tubing in dual completion systems. Oxygen activation technique (or Water Flow Log, WFL), was successfully used to diagnose these problems. Subsequent workovers resulted in significant production increase, confirming the answers obtained from these surveys. Unlike some other tools, oxygen activation log is immune to well deviation. It therefore works equally well in vertical or deviated holes. It further reacts to flowing water only. Thus standing water or any non-water fluids are simply neglected by this measurement. Being a nuclear technique its depth of investigation extends behind the pipe. This property allows us to monitor water movement in cement channels or behind tubing in dual completion injectors. This paper explains the principal of oxygen activation log and shows its two important applications. Introduction In traditional production logging, spinner flow-meter measures the average fluid velocity of all phases. This is combined with a holdup measurement, such as density, to determine velocity of each phase. Frequently we come across situations where this procedure cannot be used,The measurement sensors in conventional measurements must be in direct contact with the fluid to be monitored. This is not possible when we want to monitor water movement behind casing, e.g., in cement channels (Fig. 1) or in dual completion wells (Fig. 7).In deviated wells, the spinner is often biased towards the fluid flowing on the low side of the hole. The fluid velocity of this heavy fluid is less than the average fluid velocity in the bore-hole. In extreme cases this fluid can be stagnant or flowing in opposite direction to normal flow. In most of the cases, the spinner will underestimate the fluid velocity in high deviation or horizontal wells.Since the slippage velocity curves cannot be used in horizontal wells, a direct measurement of phase velocity and holdup is needed to solve such multiphase flow problem. This has been the subject of a number of papers presented in the recent past (Ref. 1–4). A special set of tools have been developed to address these needs. This, however, is not the subject of this paper. In GOS wells, we faced the first two limitations of conventional log that were adequately solved with WFL. While oxygen activation log was used standalone in the examples presented in this paper. It is also being used in conjunction with other measurements to solve multi-phase flow problems in horizontal wells. Principle of oxygen activation log The physics of oxygen activation measurement is described in Fig. 2. This measurement is made with a pulse neutron tool by making a series of 2 or 10 second neutron bursts. Some water in the vicinity of minitron is activated every time the neutron burst is made. The activated water is detected by -detectors placed at 1 ft, 2 ft or 15 ft depending on the velocity of water. The travel time of activated water from minitron to the detectors provides water velocity knowing the space between minitron and -detectors. The oxygen in water is activated after absorbing a neutron emitted from the minitron of the pulsed neutron tool. The activated oxygen returns to its stable state by emitting a -ray. The half life of this reaction is about 7.1 seconds. Slow moving water may not be detected by -detectors at 15 ft as most of the water would deactivate before reaching there. The slow moving water is instead detected by -detectors present at 1 ft or 2 ft. Thus by using three different detectors a range of water velocities can be covered. P. 493^

The consequences of sand production are often disadvantageous to the short and long-term productivity of the well. Although some wells routinely experience controllable sand production, these are the exception rather than the rule. Sand production and its management over the life of the well is not an attractive situation but is often essential to extract the resource. Knowing the root cause behind sand inflow in a well and the possible results can inform an appropriate strategy to safely extract as much of the resource as possible. The sands in such reservoir units often have high permeability and are mechanically weak and prone to sand production. The producing wells are often completed with gravel-packed completions for efficient sand control. Most of the wells have multi-zone completions for better productivity but this further complicates reservoir characterization. This paper describes the first use of downhole sand impact detection technology in such fields. The sand detection technology integrates the fully digitized high-resolution acquisition with signal processing and interpretation algorithm to enhance the sand particle detections as small as 0.1 mm in diameter and up to 1,500 impacts per second. The tool is designed to immune the sensors from any background noise and gas/liquid jetting effect. A combination of production logging tools (PLT) and the sand impact detection tool, was used to understand four phase zonal contributions (gas, oil, water and sand) and pinpoint sand entry in these cases. Results exceeded expectations and the ability for the sand detection tool to accurately detect the point of sand entry enabled immediate intervention to eliminate sand production in these case studies. One of them also resulted in increased production of 7.4kb/d oil without any sand flow and with greatly reduced gas-oil ratio as compared to pre-intervention production. The work clearly demonstrates the practical and effective use of downhole sand impact detection with new sand detection technology to identify and isolate sand production in wells. The innovative tool design makes it feasible to detect even small sand particles in adverse wellbore conditions and varied production rates, thus adding a detection of the fourth phase in an otherwise three phase production log.