Partially dehydrated-gelled drilling fluid and filter cake must be displaced from the wellbore annulus to achieve a successful primary cement job. A term 'Erodability of drilling fluid' is defined in this paper and was calculated from measured parameters in a large-scale test model. Differential pressures were measured in the annular space between the casing and a man-made, permeable formation and also inside the casing. Three different drilling fluids used in typical field operations were tested. Each drilling fluid was tested over a period of four days. Experimental data on erodability of drilling fluid filter cake is presented as a function of time, flow rate, and aging. A mechanism is proposed for the erosion of partially dehydrated-gelled drilling fluid and filter cake. Recommendations are given to improve the removal of partially dehydrated-gelled drilling fluid and filter cake and thus achieve a successful primary cement job in field operations. Michaels et al .,8 Outmans,a Potanin et al.,lo and SPE 24571

Horizontal wells present an effective method to maximize production potential and reduce development costs of some oil and gas fields. The ability to predict induced fracture direction with reasonable accuracy can allow the operator to drill in the direction considered most profitable.1 Ideally the well would have extended reach in the proper direction through a stable, fractured formation, would not require stimulation, and would not be subject to the production problems usually encountered in the life of a field. Since horizontal wells are drilled in a variety of formations, operators are experiencing the normal well problems and are finding stimulation and control methods useful for production improvement. This paper will examine problems associated with cementing of horizontal sections and the recent technology advancements that may be applied to help assure a competent annular hydraulic seal. Conventional cemented completions have not been used extensively in horizontal wells since some operators lack confidence in the technology that is available. Problems have been perceived in managing cuttings transport, pipe centralization, effective mud displacement, cement free-water control, and effective placement of a cement seal around the casing. These problems do exist and corrective techniques are complicated by highly deviated wellbores, but technology advances have been made to address horizontal conditions. Proper cementing may continue to provide an economical hydraulic seal for zonal or wellbore segment isolation so necessary to effective stimulation and work-over operations. The use of advanced technology often requires extensive pre-planning and includes the necessity to properly communicate the benefits to field operations personnel to assure the proper implementation of new or different techniques or materials. Little good will come from the best ideas without proper follow-through during application.

Previous research has demonstrated that proper hole conditioning is critical to successful cementing operations. However, in the past, there has not been a reliable technique available to the industry to continuously monitor the volume of hole circulating. Liquid calipers (tracers) are difficult to run and cannot be run continuously to know how the well is cleaning and when the well is ready for cementing. PURPOSEThe purpose of this work was to investigate the feasibility of estimating the percentage of hole circulating during hole conditioning by a continuous real-time method. This method consists of carefully monitoring surface pressure, fluid flow rate, fluid properties, geometry, and temperature to estimate hole size and circulatable hole.

This paper describes the design, development and application of a new sealant system for multilateral well junctions. The sealant system has been successfully applied in offshore multilateral well installations for North Sea operators. In recent years, the oilfield industry has shown an increasing interest in multilateral wells. Multilateral wells are an economically viable solution for many offshore operators because multilateral wells increase reservoir drainage and extend the wellhead slot coverage on offshore platforms. Multilateral wells can range from simple openhole completions to sophisticated cased-hole completions that have selective access to all laterals. In contrast to the openhole completions and slotted-liner completions, cased-hole completions enable the operator to have more control over production because cased-hole completions allow re-entry for perforating and production logging operations. However, zonal isolation is difficult to achieve at a multilateral junction where the hydraulic seal between the formation and the casing interior is maintained by the sealant only. The sealant system must be resistant to many destructive forces during completion and production. Mathematical models were used to quantify stresses that are exerted on the sealant during completion and operational processes in a multilateral well. A procedure was established to scale the stresses to laboratory conditions. Based on the procedures, it became apparent that the multilateral sealant required high elasticity and high impact resistance, as well as standard oilfield cementing properties. This paper presents how the sealant system was specifically designed and developed to meet the requirements of a cased-hole multilateral completions. Field jobs in which the sealant system was successfully placed are presented. These jobs show that the sealant system withstood stresses at the junction in North Sea multilateral completions. Introduction Multilateral wells have recently been developed to increase production. Multilateral wells can be vertical or deviated (including horizontal) wellbores connected to one or more subordinate laterals. Drilling and completion equipment have been developed that allow multiple laterals to be drilled from a main cased and cemented wellbore. Each of the lateral wellbores can include a cemented liner that is connected to the principal wellbore (Figure 1). Multilateral wells have been successfully drilled and operated; however, one operational problem involves zonal isolation of the multilateral junction. The casing and liners are cemented in the principal and lateral wellbores, respectively, by introducing cement slurries in the annular clearances between the walls of the wellbores and the casing and liners. In the past, conventional well cement slurries were used. Although cement is a strong material, it cannot withstand repetitive impacts and stresses that occur during drilling, milling and other well operations in the laterals. Once the set cement is shattered, it may allow leakage of fluid through some portions of the wellbores. Improved methods of cementing multilateral wells were necessary. A sealant research project was initiated to determine testing methods and fluid compositions. A number of test methods were used including API fluid testing, impact resistance tests and chemical resistance tests. The multilateral sealant required high elasticity and impact resistance. Therefore, a highly elastic sealant and a brittle sealant were chosen as extremes to guide the development of the multilateral sealant. Elastomer-based slurries were chosen for testing because they are known to provide high elasticity to set materials. P. 243^

Zonal isolation in injection, geothermal, and producing wells is critical both to reservoir evaluation efforts and to operations, but often, cementing between the casing and the wellbore is still the only method of zonal isolation performed in many wells. Although zonal isolation and well diagnostics techniques have improved, primary cementing techniques may be inadequate for some reservoir conditions, resulting in undesirable water flows, gas flows, or both. If zonal isolation is inadequate, then expensive, often complicated remedial cementing work will be needed for improved well and reservoir performance. If conformance technology is applied during the drilling phase, it can improve the performance of primary cementing processes, making them safe and economical. Conformance treatments seal problem intervals before primary cementing, thereby alleviating potential well-control problems. These treat-ments also help ensure successful primary cementing operations and prevent isolation loss caused by the casing expanding and contracting during production-pressure cycles. The formation itself, rather that the cement sheath alone, becomes the zonal isolation mechanism. During the drilling phase, zonal isolation requires the use of coiled tubing, a hydrajetting device, a depth-correlation device, and a sealant. The sealant should be water-thin during placement, and should become an elastic polymer only after it is set in place. This zonal isolation technique requires an understanding ofdepth correlation to open hole logs, through the use of mud-pulse technology, andhydrajetting techniques that remove mud filter cake while placing the sealant. This paper presents examples of this technique for a 7 7 /8-in. wellbore and a 13 1/2-in. wellbore. Introduction The creation of an effective reservoir management strategy requires an operator to achieve zonal isolation, model past-production performance, and predict applied technology's influence on future production performance. Satter and Thakur1 state that the current challenges to effective reservoir management areimproved definition of reservoir characteristics,improved tracking of fluid movements through the reservoir, andimproved control of fluid movements in the reservoir. Reservoir diagnostics and performance predictions require the complete isolation of the intervals under evaluation, and conventional zonal isolation methods have proven inadequate for many reservoir-related conditions. Zonal isolation failure after primary cementing operations has often been attributed to the ineffective removal of drilling fluid filter cake. As early as 1940, large-scale displacement studies presented by Jones and Berdine2 discussed the difficulty of removing drilling-fluid filter cake from the face of a permeable formation. The studies concluded that a deposited filter cake was removed most effectively by scrapers, the hydraulic impingement of fluid jets, and acid treatments. Since 1940, the industry has spent millions of dollars studying the mud displacement process. Many industry-wide best practices have been established based on the results of this research. Even with these advances, some formations present significant challenges during drilling, primary cementing operations, and production or injection operations. These challenges often cannot be corrected when conventional best practices are applied. Sweatman et al.3 list the following challenges that the industry is currently facing:shallow water flowsgas- or water-cut drilling fluid and cementgas hydrates in the drilling fluidformation sloughing or hole collapse during drilling or open hole production