TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractRelatively heavy crude production has historically been a problem in vertical completions in mature and new development fields in the Gulf of Mexico. Horizontal wells have been utilized to minimize water coning in potential completions that are close to the oil/water contact. However, horizontal completion costs are typically 60% more than vertical completions, consequently well and fluid design are critical to minimizing costs associated with drilling (fluid losses, wellbore stability, etc.). In addition to the engineering challenges for horizontal drilling, formulating a reservoir drillin fluid (RDF) that minimizes invasion and fluid losses to the reservoir, provides compatibility between the reservoir fluids and the RDF fluid, and readily cleans-up is critical to success. This paper will demonstrate the use of sidewall and conventional core material and subsequent petrophysical techniques to design a compatible RDF system. Core material from offset wells and previous vertical wells in several sands were utilized to develop bridging-material blends, determine sorting, texture, and particle and pore size. The authors discuss the advantages and disadvantages of using this type of material as well as that of a relatively new computer technique that allows a pore-size distribution to be rapidly calculated from core material. Another technique utilizes the rock attributes and log information in conjunction with a rock catalog to facilitate rapid determination from analogs. This type of data, in turn, can ultimately be utilized to design an RDF system. As such, this method will also be described and contrasted with traditional methods.Finally, case histories from several recently drilled horizontal wells that incorporated the subsequent RDF bridging-solids design using the aforementioned techniques will be presented. Fluid losses and solids loading will be examined with respect to the RDF designs.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper summarizes the systematic methodology & engineering process employed to identify and refine the highly effective fluid-train solutions used to drill, and install the highly productive, long horizontal gas well completions of the NCMA Hibiscus Project offshore Trinidad. It presents and discusses the unique fluids design, pre-project evaluation, and the integrated application efforts undertaken to: 1.) Minimize formation and completion damage; and 2.) Maximize gravelpack placement and filtercake removal efficiencies. The paper will identify important reservoir drilling and completion fluid service integration points (metrics), laboratory validation methods employed, and provide completion process details that led to the successful high-rate gas well installations in an unconsolidated sandstone reservoir.Specific topics discussed will include: the design and implementation of: the optimized Reservoir Drilling Fluid (RDF), RDF to Completion Fluid displacement, gravelpacking process, and the filtercake removal treatment. Finally, the paper will present case histories of the five completions installed in the Hibiscus reservoir and provide comparisons of: 1.) RDF drilling performance, 2.) gravelpacking efficiency, and 3.) well performance (productivity) of a stand-alone screen completion versus the gravel packed wellscreen completions that employed the unique RDF and filtercake cleanup treatments.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractEven though drill cuttings are first hand actual reservoir information, their conventional analysis during mud logging is limited and under estimated as source of relevant information. Drill-in fluid design becomes successful if bridging materials such as sized salt or calcium carbonate is matched with pore geometric attributes of formation rock.A novell approach for drill cuttings analysis is being under use to select the optimum sizing for bridging material, when there is no core information available.After using a combined technique of Scanning Electron Microscopy (SEM), chemical analysis by Energy Dispersive X ray Spectroscopy (EDS) and Backscattered Electron Images (BSEI) digital processing and analysis, it is possible to get key parameters to design a more efficient Drill-in fluid. It can help also in the selection of screens for solids control in surface equipment.Textural parameters found with this technique include grain size distribution, shape and sorting. Porous space description such as (2D) porosity and pore throat size distribution, that can be obtained in grain clusters coming from drilling consolidated rock horizons. Rock fracturing trends, natural or induced can also be observed. Therefore a more detailed sample description is achieved in relation to conventional analysis.Once this information has been processed, laboratory filtration tests can be performed on available reservoir or similar synthetic material, in order to recommend a better formulation of Drill-in fluid for field use.

Casing centralization and reciprocation during a cementing operation can help improve the efficiency of annular mud displacement and provide a basis for analyzing the percentage of mud displacement efficiency. This information is necessary when developing a mitigation plan for any cementing operation's risk assessment when centralization and pipe movement are considered as operational variables. A state-of-the-art, three-dimensional (3D) finite displacement efficiency simulator analyzes the percentage of mud displacement efficiency when these four main possible scenarios are considered: low, medium, and high centralization and casing reciprocation during the cementing operation. This paper discusses three case studies validated by a risk assessment process developed during the cementing job design stage in which higher standoff and casing reciprocation suggest improved mud displacement efficiency and low fluid channeling when the cementing operation is finished. Cement bond log (CBL) results are discussed and shared when high standoff and casing reciprocation scenarios are considered. Results of this study include the following observations and conclusions: Casing reciprocation helps improve displacement efficiency, which can provide improved cement bonding.If casing reciprocation movement is not possible, high casing centralization standoff can be an effective design technique because it can be used to enhance mud displacement efficiency in cementing operations. Wellbore stability is not compromised by equivalent circulating density (ECD) increments resulting from the reduction of annular clear space when using centralizers.Design risk assessment should include a comparative scenario analysis to mitigate the potential risk of poor mud displacement efficiency when considering casing centralization with medium to high standoff and casing reciprocation.At some point, casing reciprocation will not be a factor of improvement for mud displacement efficiency when sufficient standoff is considered for cementing operation designs. This scenario can help mitigate any likelihood of poor mud displacement efficiency if the casing is not reciprocated because of operational factors.Even though high casing standoff yields high percent displacement efficiency, it is recommended to follow the primary cementing operation's field practices as discussed. A comprehensive practical analysis to prepare a cementing risk assessment included in an operation's program is reviewed. It considers low and high casing centralization as well as pipe movement as variables to help improve cement placement.

ABS1RACfMineralogical and pore characterization has become an important key when evaluating oil reservoir quality. Presence of diagenetic or secondary mineral such as clays and cementing material can modify rock's texture, affecting in many cases the porosity and permeability during production and EOR processes.Scanning electron microscopy (SEM) and other related techniques have been widely used in petroleum industry to study and characterize sedimentary rocks.Backscattered electron (BSE) detectors and X-ray analysers are tools generally associated with SEM instruments, used by petrographers and petrophysicists who have taken a deeper concern with rock porous media (texture and mineralogy) through micrographies (analog signal) and its processing (digital signal). Relation between mineral composition and gray tone in the original signal, results on what could be called BSE imaging technique which shows some advantages over conventional techniques.Core samples from Venezuela western region have been evaluated by BSEI. Micrographies from a SEM, working in the BSE mode were digitized and processed whith PDIFRAC software which was developed for this purpose.References and illustrations at end of paper 153 Mineral and porosity fractions of the cores are presented for different depths. These results are compared with results obtained previously by XRD, IR and thin section petrography on the same samples.Images are used to provide mineralogical composition, porosity maps, fractal dimention calculations and to visualize potential cases of formation damage by fines migration (kaolinite and pyrite fines) IN1RODUCfIONSedimentary rock characterization is an important step in activities such as exploration, drilling, stimulation and enhanced oil recovery, mainly because the nature of that kind of rock (geometry and mineralogy) will define the specific treatment to be given to the reservoir 1.The aim of this work is to show preliminary results of a proposed technique for sedimentary rock characterization, based upon the analysis of digitized images obtained by scanning electron microscopy (SEM) in the backscattered electron mode.Conventional SEMs bring the options of X-ray analyzers and backscattered electron detectors (BSE). The first give chemical information as elemental composition in a mineral and the former gives mineral phase information directly due to the relation between intensity of the signal output and average atomic number in a mineral, consequently different minerals have different gray tone images 2 Oil Reservoir Sandstones Evaluation with Digital Backscattered Electron I Images SPE 23667 on the microscope· CI'R. At this point image analysis plays a fundamental roll.Mineralogy is a parameter that can be determined by other techniques such as thin section petrography, infrared absortion and X-ray difraction. Somehow this techniques give a limited information about the atributes of the porous space (geometry, grain size distribution) and as in the case of thin section petrography a subjective approach is given.Hav...