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The SP curve is a continuous recording vs. depth of the electrical potential difference between a movable electrode in the borehole and a surface electrode. Adjacent to shales, SP readings usually define a straight line known as the shale baseline. Next to permeable formations, the curve departs from the shale baseline; in thick permeable beds, these excursions reach a constant departure from the shale baseline, defining the "sand line." The deflection may be either to the left (negative) or to the right (positive), depending on the relative salinities of the formation water and the mud filtrate. If the formation-water salinity is greater than the mud-filtrate salinity (the more common case), the deflection is to the left.
When invasion is moderate to deep, knowledge of resistivity of the invaded zone (Rxo) is required to derive the resistivity of the uninvaded zone (Rt) from the deep-resistivity measurement. To evaluate a formation with logs, the Rxo/Rt ratio is required for some saturation-estimation methods. In clean formations, a value of the formation resistivity factor F can be computed from Rxo and Rmf if Sxo is known or can be estimated. Tools designed to measure Rxo have a very shallow depth of investigation, because the flushed zone may extend only a few inches beyond the borehole wall. To avoid the effect of the borehole, a sidewall-pad tool is used.
Fluid-Loss-Control Additives (FLAs) are used to maintain a consistent fluid volume within a cement slurry to ensure that the slurry performance properties remain within an acceptable range. The variability of each of these parameters (slurry performance properties) is dependent upon the water content of the slurry. If the water content is less than intended, the opposite will normally occur. The magnitude of change is directly related to the amount of fluid lost from the slurry. Because predictability of performance is typically the most important parameter in a cementing operation, considerable attention has been paid to mechanical control of slurry density during the mixing of the slurry to assure reproducibility.
Resistivity logging is an important branch of well logging. Essentially, it is the recording, in uncased (or, recently, even cased) sections of a borehole, of the resistivities (or their reciprocals, the conductivities) of the subsurface formations, generally along with the spontaneous potentials (SPs) generated in the borehole. This recording is of immediate value for geological correlation of the strata and detection and quantitative evaluation of possibly productive horizons. The information derived from the logs may be supplemented by cores (whole core or sidewall samples of the formations taken from the wall of the hole). As will be explained later, several types of resistivity measuring systems are used that have been designed to obtain the greatest possible information under diverse conditions (e.g., induction devices, laterolog, microresistivity devices, and borehole-imaging devices). Many service companies offer resistivity-logging services, and most offer a Web-based catalog ...
Alsaba, Mortadha (Australian College of Kuwait) | Al Mejadi, Mohammed (Kuwait Gulf Oil Company) | Fahmy, Mohamed (Australian College of Kuwait) | Aldarakh, Yousef (Kuwait Energy) | Farhat, Ali (Australian College of Kuwait) | Majli, Jaber (Al-Meer Technical Services)
Abstract Drilling fluid severe losses through highly fractured or highly permeable formations is considered as one of the most critical problems while drilling through these problematic zones, which can result in a costly non-productive time (NPT), and might lead to catastrophic well control issue in worst-case scenarios. The effectiveness of LCM treatments is often evaluated in the lab prior to field application. The main objective of this paper is to present the development of an in-house testing apparatus that simulates and evaluate the effectiveness of a proprietary LCM pill in curing losses through highly permeable formation. A testing apparatus was developed in-house to simulate and evaluate the effectiveness of a proprietary LCM pill in curing losses through highly permeable formation. The apparatus consists of a transparent testing cell, which simulates the filtration medium, to visualize the losses profile through a gravel bed with porosity up to 40%. Four different blends at different concentrations (between 9 – 17 lb/bbl) were mixed in a 7% bentonite mud and evaluated at 100 psi using the newly developed apparatus. The depths of fluid invasion, the fluid loss, and the filter cake thickness were measured accordingly to evaluate the effectiveness of the developed LCM pill. The testing apparatus was successfully built, pressure tested up to 150 psi, and used to evaluate the developed LCM pills. The results showed that the developed blends were able to plug and seal the highly permeable filtration medium effectively. The evaluated LCM pills resulted in a depth of invasion ranging between 44 – 96 % of the total length of the filtration medium and a filtrate volume of less than 5 ml/30 min depending on the concentration of the additives used. The filter cake thicknesses ranged between 0.16 – 1.37 inches, where the best blend resulted in the thickest filter cake. Based on the results, the blends showed a superior performance in terms of curing the losses in a short period of time, which in turns will contribute towards reducing the associated NPT and further unwanted consequences.
Al-enezi, Dakhil (Kuwait Oil Company) | Al-salamin, Mohammad (Kuwait Oil Company) | Sulaiman, Sulaiman (Kuwait Oil Company) | Muqaddas, Zahraa (Kuwait Oil Company) | Al-shelian, Jasim (Kuwait Oil Company) | Fahmy, Moustafa (Kuwait Oil Company) | Alrashoud, Ahmed (Kuwait Oil Company) | Gholoum, Ali (Kuwait Oil Company) | Almarshad, Mubarak (Kuwait Oil Company) | Ibrahim, Ahmed (Baker Hughes, a GE company) | Alotaibi, Ali (Baker Hughes, a GE company) | Sheer, Shahad (Baker Hughes, a GE company)
Abstract It is a challenge to drill a highly deviated or horizontal hole in high permeable formations. High differential pressures may lead to several problems like tight holes, wellbore instability, differential sticking and mud loss while drilling across these permeable or fractured formations. It was always preferred to drill these wells with Oil base muds which showed some success. While operators always prefer the standard solution, which is casing isolation for problematic sections, challenges have increased due to continuously drilling in depleted reservoirs which leads to considerable nonproductive time. The other solution to overcome such problematic sections was to re-design a fluid system that would target drilling through serious of highly permeable sand and shale formations. The fluid system would primarily address shale inhibition along with effective bridging, minimizing pore pressure transmission and wellbore strengthen with increased hoop stress in the wellbore. Software modelling and permeability plugging tests were performed to evaluate the fluid behavior under downhole conditions and to predict the characteristics of induced micro fractures based on rock mechanics. Porosity, permeability and induced micro fractures were considered to optimize the bridging mechanism. It was identified that normal bridging solutions involving calcium carbonates and graphite material were not enough to address the pore pressure transmission problem. It was essential to include a micronized sealing deformable polymer along with normal bridging material was effective in plugging pore throats and minimizing fluid invasion. The deformable polymer component is able to re-shape itself to fit a broad range of pore throat sizes which was previously unattainable with conventional bridging technology which was confirmed by particle plugging tests. A one well was identified to be drilled in highly depleted reservoir at an inclination of almost 45 degrees. The section involving the highly depleted and permeable sand involved drilling highly stressed shale formations which requires high mud weight for their stability. This was the first attempt on a high-angle well with development drilling operations in Kuwait and was performed to facilitate the successful drilling of the reservoir. Drilling and logging were successfully performed along with logging and LWD runs with no recordable differential sticking or losses incidents. This paper also presents 2 successful applications in the same field with the application of proper bridging and utilization of deformable sealing polymer to address drilling problems through highly depleted and permeable formations while managing over balance of 3500 psi across them.
Abstract This paper chronicles cases histories both on land and offshore environments that demonstrates the efficacy of different lost circulation systems and products that are used either individually or cooperatively to mitigate losses ranging from severe to partial. The application of different systems and products for losses stemming from highly permeable formations, weak formations, and natural fractures are discussed. Simulated software results and laboratory test data are also presented, providing quantitative and qualitative evidence. The paper covers a review of cement jobs undertaken over the past 2 – ½ years commencing in 2013. These jobs cover land operation in Kazakhstan as well as operations in the Caspian Sea offshore Azerbaijan. The severity of the losses encountered ranged from anticipated to upwards of 90% prior to cementing. Various lost-circulation control techniques are analyzed, ranging from the use of novel cement spacers, inclusion of fiber products within the cement slurry, pumping alternative non-portlandite cement materials, or combining those technologies. In some cases, post-job hydraulic analysis of the downhole equivalent circulating densities encountered will be used to validate the success of the techniques. Laboratory data from tests attempting to simulate the downhole fractures and sealing properties will also be included, providing quantitative and qualitative evidence of the need for further investigation in the application of various fibrous materials. Over the course of the jobs, it became quite conclusive: ➢The use of novel cement spacers including additional fiber /solids can reduce losses in circulation by 100% or in the case where losses were anticipated while cementing, results with no losses at all and cementing objectives being achieved. This application covers cases where there were losses upwards of 20 bbls per hour before commencing the cementing operations. ➢Lost-circulation plugs using a non-portlandite system can successfully stop losses while drilling, allowing for subsequent RIH and primary cementing operations. ➢The Portland cement is an excellent lost-circulation control material by itself. However, the results will show cases where microfractures are induced during the primary cementing operations due to relatively low fracture gradients. The use of fiber elements within the cement slurry will assist in sealing the micro-fractures, preventing catastrophic losses during the cement job. Lab tests simulating micro-fractures up to 6 mm demonstrate that they can be sealed off by adding fiber and solid materials to the cement slurry. ➢Proper research of historical files and jobs conducted within an area helps the drilling team assess the potential risks and pre-plan to mitigate such risks. Combinations of the various loss circulation control techniques can then be factored into the design. One case history documents this approach, leading to the successful achievement of the cementing objectives. ➢The holistic, data-driven approach is an ideal way of selecting lost-circulation materials and should have applicability as a best-practices approach around the world. The holistic, data-driven approach is an ideal way of selecting lost-circulation materials and should have applicability as a best-practices approach around the world.
Roohi, Abbas (Montanuniversität Leoben) | Elmgerbi, Asad (Montanuniversität Leoben) | Nascimento, Andreas (Montanuniversität Leoben) | Prohaska, Michael (Montanuniversität Leoben) | Thonhauser, Gerhard (Montanuniversität Leoben)
Abstract Historically Reaming While Drilling (RWD) operations have been restricted to softer formations. The objective in this study is to create a thermoporoelastic model of Mechanical Specific Energy (MSE) for RWD in order to shed important new light on the decision process how to use RWD for a specific formation as well as a recommendation for reamer-pilot size ratio. The analytical approach developed in this paper calculates thermoporoelastic coupled time-dependent stress, pore pressure and temperature variations for an inclined borehole that is drilled through permeable or impermeable formation and which is subjected to far field three dimensional in-situ stresses. Apparent rock strength of the rock in Depth of Cut (DOC) zone beneath the reamer can be determined by using Mohr-Coulomb theory. By using Apparent Rock Strength (ARS) the analytical Mechanical Specific Energy (MSE) can be estimated afterwards. This parameter can be used as a key decision to determine whether a specific formation is a good candidate for RWD or not. A proper combination of pilot and reamer is absolutely critical to optimize bottom hole assembly (BHA) performance and durability. For many years, a trial-and-error technique has been employed by the drilling industry to determine advantages or drawbacks of reamer in the BHA and the optimum reamer-to-pilot-size ratio and bit characteristic for drilling, which requires a significant investment of time and money. The comparison of reamer's MSE, to destroy rock around the wellbore, with bit's MSE, to destroy rock at the bottom of the hole, shows how efficiently reamer can drill rock around the wellbore in certain formation, and in some other formations the drawbacks are outweigh of its advantages. This in turn makes it possible to determine proper formation characteristics to employ reamer in the BHA and also the maximum reamer/bit size ratio for certain rock characteristics in order to support efficient drilling operations. Considering that so fare in the market there is no evidence of a specific model to predict rock strength bellow the reamers, this research and study show its degree of novelty since it propose a model to fill this gap, which can in the future and after tuning be used as a reference application in the petroleum industry for decision making and project cost analysis. Validation in different environments is still to be concluded as a next step in this research.
Bageri, B. S. (King Fahd University of Petroleum & Minerals) | Mahmoud, M. A. | Al-Mutairi, S. H. (King Fahd University of Petroleum & Minerals) | Kuwait, Chevron (King Fahd University of Petroleum & Minerals) | Abdulraheem, A. (King Fahd University of Petroleum & Minerals)
Abstract The filter cake evaluation involves many comprehensive testing and procedures to determine the filter cake properties such as thickness, mineralogy, porosity, permeability, and filtration to design the optimal mud program. For the maximum reservoir contact (MRC) and extended reach (ER) wells where the horizontal section could be 3000 ft or more in those wells, the filter cake formed by the drilling fluid varied from one section to another in the long horizontal section. Therefore, the process of filter cake removal in maximum reservoir contact and extended reach wells should consider the variation in the filter cake properties to achieve an efficient removal process. This research focuses on evaluating the filter cake porosity and permeability profile through the horizontal wells. Moreover, the impact of the filter cake porosity and permeability on the removal process is presented in this work. To achieve the objective of this work, high pressure high temperature (HPHT) fluid loss test was conducted to form the filter cake using actual drilling fluid samples. The compositional and structural analysis of filter cake was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-Ray Fluorescence (XRF). The drilling fluid studied samples were collected from real field rig while drilling the horizontal section. The results showed that the drilling operation was initiated with drilling fluid that was capable of forming a filter cake with low porosity (5 %) and permeability (0.01 md) to minimize the filtration volume. In the first part of the horizontal section the filter cake porosity and permeability increased sharply as more feet of horizontal section drilled. The porosity increased to about 35% and permeability to 0.25 md. After that it remains stable with slight decrease. This growth in the filter cake porosity from 5 to 35% reduced the liquid to solid ratio in the removal process from 28 gm per 500 ml up to 18 gm per ml. The result of this work linked the filter cake properties (thickness, porosity, and mineralogy) in the maximum reservoir contact and extended reach wells with solid to liquid ratio needed to be used in the filter cake removal process. This work will help to reevaluate the filter cake removal and stimulation recipes that were designed based on constant filter cake properties.
Summary Formation-pressure integrity tests (FPITs) are used to verify the integrity of cement at a casing shoe, measure the stress state of the exposed formations for well planning and operations, and determine the maximum equivalent circulating density to which a shoe can be safely exposed. Critical decisions on operations are made directly from the results and include decisions about the need for remedial cement operations, maximum mud weights that can be used to drill the next well section, minimum mud weights that can be used to prevent hole collapse, calibration factors for predicting fracture gradients, and the potential need for lost-circulation-mitigation strategies. The interpretation techniques of the result most frequently focus on the point at which a fracture first starts, the point at which unstable fracture growth begins, or the closure pressure of the fracture when pumping ceases. However, the early pressure-buildup behavior is often overlooked and can provide much insight on the integrity of cement, the point of the start of a fracture, the permeability of the formation being tested, the need for cement remediation, and the potential to increase fracture resistance by use of wellbore-strengthening techniques. This paper presents a model for predicting early pressure-buildup behavior, discusses how the model can be used to improve the interpretation of FPITs significantly, and provides examples of the application in select wells.