TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractIdeally, a reservoir drill-in fluid (RDF) possessing both an oil external phase for drilling and a water external phase for completion would provide the ideal solution for drilling and completing a well. Through the manipulation of surfactant chemistry, a novel reversible invert emulsion drilling system, which provides both attributes, has been developed. During drilling, an operator can utilize the reversible oil-based mud to take advantage of the commonly accepted properties that enhance the drilling efficiency and then convert this system to a water-based fluid to improve the completion efficiency.The amine-based surfactants used in the reversible invert system are strong emulsifiers in an alkaline medium; however these same emulsifiers become more common direct oil-inwater emulsifiers in the presence of protonating agents such as acid. This process of protonation and deprotonation of emulsifiers controls the emulsion phase of this drilling system and thereby, the oil-wetting and water-wetting characteristics of the subsequent filtercake and entrained solids. As the bridging agents in filtercake are commonly calcium carbonate, once water-wet (in presence of acid) promote clean-up and thus, are readily consumed by common acids that may be utilized during the completion phase.This system was field trialed with success for drilling and completing an injector in the first quarter of 2000. Since this initial application, numerous completions have utilized this reversible invert RDF system. This system has been successfully applied to a variety of completions, in particular: injectors and producers, openhole gravel-packs (OHGP), expandables and standalone as well as various environments and reservoirs. Theoretically, this system also provides advantages with respect to common cementing and environmental issues.This paper presents the development of this multi-purpose drilling and completion system and discusses the application of this technology to adapt to the challenges of evolving global completion complexity.Several case history examples are presented from selected completions. The paper includes the laboratory pre-planning and field data illustrating the concerns and the development of a solution with respect to drilling and clean-up.
A case history from Offshore Israel is presented that describes the successful delivery of two (2) ultra high-rate gas wells (+200 MMscf/D) completed in a depleted gas reservoir with 9⅝ in. production tubing and an Open-Hole Gravel Pack (OHGP). Maximizing gas off-take rates from a volumetric drive gas reservoir that possess high flow capacity (kh) require large internal diameter (ID) tubing coupled with efficient sand face completions. When sand control is required, the OHGP offers the most efficient as well as the most reliable, long-term track record of performance. A global study of wells completed with 9⅝ in. production tubing ("big bore") determined that this design concept was feasible and deliverable in a short time frame while still maintaining engineering rigor. The paper will highlight key accomplishments within various phases of a completion delivery process for critical wells. The completions were installed with minimal issues (NPT≈ 9%) and have produced without incident. The wells are capable of +250 MMscf/D and are currently producing at +220 MMscf/D.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractControlling fluid losses to the formation, both before and after sand control completions, is critical to optimizing production. While mechanical devices, such as flapper valves, remain the preferred choices for preventing fluid loss when the service tools are removed from the production packer, they sometimes fail or otherwise cannot be used. In those instances, chemical fluid loss control pills are frequently used as supplements or contingencies. Unfortunately, this option normally requires remedial treatment that adds cost and can cause a host of additional problems, not the least of which is the risk of formation damage. This paper describes the development of a uniquely engineered fluid-loss control pill, designed for placement inside the gravel pack screen and that has been shown to effectively control fluid loss without the subsequent need of remedial treatment. The authors demonstrate that optimizing the particle size distribution of the bridging particles within the fluid loss pill for specific screen types deposits a surface filter cake against the inside surface of the gravel-pack screen assembly. Complementing the development of the fluid loss control pill, which can be pumped at comparatively small volumes, is a proprietary additive specifically designed to reduce the adhesive forces to metal or rock surfaces and which allows complete cake removal, using only production as the flow medium.The laboratory developmental program and a large-scale screen-flow model designed to simulate pill deposition on various gravel-pack screen types are described. Further, through field experiences, the authors will document the ability of these fluid-loss control pills to produce near zero skin and maximize production without the need for costly and risky remedial removal treatments.
The use of enzymes as an external breaker for removal of xanthan based filter cakes has exhibited cost savings and effective clean up in several open-hole horizontal Gulf Coast wells. Enzymes are specialized proteins produced by cells of living organisms. They act as catalysts to promote specific reactions. Polymer-specific enzymes hydrolyze xanthan resulting in non-damaging fragments. As a catalyst, the structure of an enzyme is unchanged by the reaction it promotes; therefore, the enzyme has the ability to initiate another reaction. The reactivity of the enzyme is essentially infinite with the exception of damage to the enzyme by chemical, thermal, or mechanical means, i.e. denatured. Xanthan-specific enzymes degrade or cleave either the a - 1,2 or ß - 1,4 glycosidic linkages of the substituent and the ß - 1,4 linkages of the backbone. Recent laboratory investigations revealed several factors, which can control the effectiveness of an enzyme. These factors include xanthan quality, iron, base brine and hydrocarbons. These factors can function as barriers and prevent the enzyme from cleaving specific linkages of the xanthan structure. This study presents guidelines for formulating an enzyme compatible xanthan based drill-in fluid for open-hole horizontal completions. These guidelines were recently applied to two recent open-hole horizontal completions in the Gulf of Mexico that yielded optimum results. Introduction Drill-in fluids are typically comprised of starch, xanthan, and sized calcium carbonate or salt in a base brine. Although, drill-in fluids are inherently less damaging than the conventional drilling muds, relatively impermeable filter cakes are still deposited on the borehole walls. Partial removal of drill-in fluid filter cakes can significantly impede flow at the wellbore wall. This can result in significant reduction of the well productivity or injectivity. To realize the full potential of open-hole horizontal completions, formation damage from residual filter-cake must be eliminated. A common approach to minimizing such damage is the application of acids or strong oxidative breaker systems to dissolve filter cake solids and biopolymers. Field experience has demonstrated that an acid/oxidative breaker performs reasonably well in short to medium radius open-hole intervals. However, an acid/oxidative breaker appears to be less effective in extended reach open-hole intervals. The problem may be related to contact time of the highly reactive solution with the drill-in fluid damage creating "wormholes".
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