fax 01-972-952-9435.References at the end of the paper. AbstractIn some Middle Eastern wells, the serious problem of shallow casing leaks results from an insufficient cement seal across a corrosive water formation containing hydrogen sulfide (H 2 S). Factors contributing to this poor seal include multiple weak adjacent zones and thin lenticular washouts, which complicate conventional cementing practices by preventing slurries from sealing off water-bearing formations and protecting the well casings. Historically, multistage cementing has only marginally improved zonal isolation in this region. High-quality foamed slurries [slurries with high volumetric concentrations of nitrogen (N 2 )] can enable coverage of the weak zone, but these slurries are too permeable to provide long-term casing protection.A joint study conducted to address casing-leak problems in a Middle Eastern field has yielded custom cement blends that mitigate the combined detrimental effects of (1) water containing H 2 S, (2) mud or whole-cement losses to lost-circulation zones (zones with very low fracture gradients), and (3) muddisplacement deficiencies primarily caused by multiple washed out sections. Successful slurries that appear (based on laboratory results) to combat these problems are foamed with nitrogen and feature a combination of Portland and pozzolan cements plus hollow pozzolan spheres. This paper discusses large-scale tests and the blends designed for these tests. Researchers conducted these tests in an attempt to prove the effectiveness of certain cement blends and to help optimize those blends. The tests show that foamed, lightweight (8 to 10 lbm/gal) slurries containing hollow pozzolan spheres with pozzolan cement can enhance the sealing of harsh-water zones. This enhancement is achieved by the combined effects of two events: (1) improving displacement of drilling mud and cuttings by optimizing foam quality, and (2) cementing past lost-circulation zones. Details of blends, test setups, and test results are discussed.
In the Arabian Gulf, a rotary-steerable system utilizing "point-the-bit" technology decreased the well-construction cost in two Saudi Arabian offshore oil fields. Drilling offshore, in many (if not all) parts of the world, is an expensive adventure. "Point-the-bit" technology has successfully and consistently controlled capital expenditures for wells in these offshore fields and, in head to head comparisons, has cost less money when compared to the conventional drilling systems that had previously been used. When it comes to offshore operational costs, time is a nemesis. The application of "point-the-bit" technology as a way to help solve this problem by permitting the economical completion of a quality borehole will be discussed in this paper. A major concern has been that the phenomenon known as "hole-spiraling" which has created hole-quality issues. These issues range from tortuous paths, torque-and-drag frictional forces, key-seating or sump effects, and poor log responses to name just a few of the problems. Thus, when the quality of a borehole and the time it takes to drill it are considered less than desirable, the drilling process and its resultant effects increase well costs and reduce operational efficiencies. Several case histories within two offshore fields will be presented in this paper. These case histories will show that having the capability to make adjustments to downhole drilling tools "on-the-fly" makes for better steering control and creates better hole geometries. Correctly applying "point-the-bit" rotary-steerable systems on these wells demonstrates the value-added potential of this technology. Introduction The price and/or cost to do business in the oil-industry for operations such as exploration, drilling, field-development, and production has continually increased over time. Even in the Middle East Region, where the cost to produce a barrel of oil is one of the lowest in the world (Fig. 1), drilling costs have naturally increased.1 This phenomena can be attributed to many factors that are connected to supply and demand which drive world market conditions. This trend to higher drilling costs is not expected to change anytime soon and is especially true when the work being performed is in an offshore environment. Because, at times cost seems to be the over-riding factor in completing a well, the condition of the borehole could suffer as a result. Operators of wells in areas that present formation, structural, or integrity related problems would undoubtedly prefer not to have borehole quality problems to deal with. Problematic hole conditions, perhaps created unknowingly, allow situations to occur that makes mechanically drilling the hole very difficult. In the past decade, considerable advancements in the drilling phase from within the drilling services segment of the industry have contributed to the reduction in operating costs for operators worldwide. Such advancements in drilling tool technology become even more important to the customer when every minute of every day is measured on the bottom line. Rotary Steerable (RST) Systems have been part of the industry for a number of years with the most recent advancement being a "point-the-bit" system known as "Geo-Pilot"®. Value Analysis Value is measured in many ways and is both quantified and/or qualified differently between organizations. Value can be specifically measured with the use of Time and Hole-Quality as a function of deliverability to the bottom line. However, even these specific measures, discussed more below, can affect each other. For example, drilling too fast, or beyond the capability to keep the wellbore clear of cuttings buildup, may create a situation where more time to ream and condition the hole is required or worse yet lead to a stuck BHA problem. Time Savings For an operator, saving time on an offshore rig is very valuable. As a result, it can be very tempting to drill as fast as possible to reach TD in order to save time. However, doing so can lead to conditions that will increase time. Being focused on increasing ROP to the point of neglecting proper hole cleaning can lead to major stuck-pipe problems.
fax 01-214-952-9435. AbstractApplications of a new slag cement and spacer system have reduced the chance of gas channels forming in the cement column during cement hydration in deep, hot south Texas gas wells. These slag cements were formulated with water and conventional cement additives to prevent gas migration and to improve interfacial bonding to oil-wet surfaces. Oil-mud removal spacer fluids (OMRS) were also specially fOlmulated to remove oily residues and improve water-wetting of the oil-wet surfaces. These OMRS can also be designed to develop compressive strength when cementing operations have been completed.Set slag cement provides a tight gas seal with shear-bond healing capacity, as demonstrated by recently developed HTHP shear-bond strength tests. The previously reported phenomenon of healing or regeneration of slag-mix bonds has been reproduced with slag cement. The rapid development of strength at the top of the long cement column and the improved bonding to oil-wet surfaces were the two major improvements provided by the slag cement. OMRS can clean oil-wet surfaces, and then set once the job has been completed.Laboratory tests and field evaluations based on cement bond logs and pressure tests indicated improved bonding and isolation of the gas zones. Field applications of slag cements and OMRS fluids have led to greater primary and plug cementing successes in south Texas gas wells, and well production economics have improved accordingly.
Wellbore construction practices are complex. Achieving dependable zonal isolation is a critical and challenging process to optimizing asset life and minimizing future well intervention. Sustained casing pressure challenges related to poor zonal isolation are well documented and can impact production that may require significant remedial well intervention. The need to address these challenges called for revisiting cementing operational practices and lead to the development of a Basis of Design (BoD) document as a tool to help manage well design practices and standards. As common industry practice to prevent fluid migration, slurry designs should be gas tight. To avoid unwanted wellbore fluids to migrate to surface, two things are required: less time to initiate migration and the lack of a flow path. With analysis of the current cement slurries, designs were unable to perform successfully on inflow tests due to low temperature of the zones to be cemented, increasing the transition time for a slurry to move from liquid state to solid phase. With extensive laboratory testing it was concluded that current designs were not addressing the bulk shrinkage phenomenon of cement, which could lead to the creation of micro annulus creating conduits for fluid migration. This paper will discuss the detailed analysis and testing of the current and new designs and techniques validated by laboratory tests and field executions (Cement Bond Logs) to prevent fluid migration and ensure that dependable long-term zonal isolation was delivered. Mud displacement mechanics needed to be optimized to reduce the risk of mud on the wall phenomenon. This included the design of spacers that increased the annulus mud displacement efficiency, improved standoff and finally optimum displacement rates to create sufficient annular velocity. A comprehensive look at all the pertinent steps in the construction of the well starting from the drilling phase, through cement job design, preparation and execution was required to ensure that the best practices are adopted to achieve the best results. Slurry selection, spacer formulation, centralization, hole cleaning and excess volumes were all at the center of the improvements that were necessary to achieve optimum results. A BoD document was developed as a roadmap for cementing to further enhance wellbore integrity. It formalized the planning, design and job execution practices and specified the slurry design, placement, and verification criteria for each casing section. Several cement jobs have been executed using the newly implemented practices that resulted in excellent zonal isolation results, which were verified through cement integrity logs. Since the implementation in all subsequent wells, no casing-casing annulus pressure issues have been reported.
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