Wellbore pressure management is a critical part of the drilling process. In normal drilling practices, static and dynamic fluid pressures are used to contain formation pressures and to assure wellbore stability. Excessive fluid pressure while circulating can create problems including reduced operating margins between fracture and pore pressures and, in the extreme, lost circulation. To address these problems, an Equivalent Circulation Density (ECD) Reduction Tool (RT) has been developed. The ECD RT is designed to counter the frictional pressure effects that exist while circulating. The tool is expected to have a broad range of drilling applications including; the narrow pore/fracture pressure margin deepwater environment, wellbores prone to instability, pressure depleted reservoirs, and extended reach wells. The tool has the potential to:Improve wellbore stabilityExtend hole intervals and reduce casing requirementsImprove well controlReduce lost circulationReduce differential stickingImprove hole cleaning in ERD wells through the use of higher flow rates This paper describes a new downhole tool for ECD reduction, which is run as an integral part of the drill string. A prototype tool has been built to operate inside 10–3/4" to 13–3/8" casing. This tool has undergone laboratory testing and full-scale technology trials are in progress. The design features of this prototype are discussed along with the laboratory test results obtained to date. Introduction This paper describes the development of a novel system for reducing the Equivalent Circulating Density (ECD) of drilling mud. The drive for reducing ECD has become apparent as the industry is faced with increasingly difficult drilling challenges. The initial focus and development for ECD reduction has been directed towards applications in deepwater. Here the issue is overcoming the significant hydrostatic pressure in the riser when it is full of weighted mud (Reference 1). However the concept affords potential benefits in a wide range of drilling applications. The work reported in this study covers the design and testing of a prototype ECD RT that in principle can be applied to a wide range of drilling opportunities (including both onshore and offshore). Benefits of ECD Reduction As the industry has strived to recover hydrocarbons in increasingly challenging areas, it has become apparent that one of the major restrictions is maintaining downhole pressures within the narrow window between pore pressure and fracture gradient. In practice, the window may become even narrower if the minimum required downhole pressure is governed by wellbore stability issues rather than just pore pressure (Reference 2). Since the size of this operating widow dictates the maximum ECD that the well can tolerate, there is clearly a big prize in reducing the magnitude of ECD. The hydrostatic head of the mud column and the frictional pressure loss in the annulus govern ECD. Therefore there are many factors that influence ECD. Conventional well designs often exploit the controlling parameters to ensure ECD's can be minimized. Such optimization methods include: reducing frictional losses through the use of low fluid rheologies; use of casing strings with wider annular clearances; the application of expandable tubulars to preserve hole size; use of drilling liners rather than full casing strings and controlled penetration rates to avoid overloading the annulus with cuttings. In addition, there are more radical methods that can be employed to reduce downhole pressures and hence ECD's. The industry has pioneered underbalanced drilling as a successful method to exploit low pressure and depleted reservoirs. Benefits in penetration rate have also been realized by appropriate application of underbalanced drilling.

Underbalanced Drilling (UBD) is becoming more widely used and accepted because of the many benefits it provides such as:Limitations to the formation damage common in regular overbalanced drilling.Increased rates of penetration.Increased production rates and in some cases production while drilling which can provide early cash flow and enhance economics. However with these advantages come some drawbacks, the chief among which is the safety of the operation while tripping the drill pipe into and out of the well. Since the well is allowed to flow in traditional UBD operations a flowing or shut in pressure results in the well.Any significant pressure at surface requires that special precautions be taken during tripping operations to control formation pressure.Several techniques can be used among which are:Killing the well, this provides for safe tripping but can obviate the very reason for using UBD - formation damage can result.Flowing the well, this can lead to a dangerous situation if a sloughing formation forms a temporary bridge in the annulus.A Snubbing unit can be employed, this enhances safety but can add considerably to the operational cost. It is clear that a better and safer method is needed, since all the above carry disadvantages, and to this end a new method involving a downhole valve was conceived.In this approach a full opening valve which can be closed below the drill string while tripping, is deployed downhole below the "pipe light" depth and operated from surface by way of a hydraulic control bundle. This paper will review the concept of the Downhole Deployment Valve (DDV), its design and operation.The authors will go on to provide details of the first field trial of the a 7" 26lbs/ft full opening valve in a multilateral well which was drilled underbalanced in the James Lime play in East Texas/Northwest Louisiana. They will conclude that this device can provide major enhancement to a UBD operation without in any way compromising its advantages. Introduction Increased awareness of the degree of formation damage caused by fluid invasion into the reservoir during conventional overbalanced drilling techniques has resulted in a growing interest in the benefits offered by UBD.These techniques, though not necessarily suitable for all reservoirs, can have a considerable positive impact in such instances as:Depleted reservoirs where in-fill wells can be drilled with little or no damage.Highly permeable and fractured reservoirs where fluid invasion can be greatly limited and consequent degradation of permeability reduced or eliminated.Hard formations where greatly increased penetration rates can be achieved. However along with the many benefits offered by UBD techniques come some disadvantages, such as higher associated costs and increased perceived risk and safety issues.Perhaps the most significant such risk is during the normal process of tripping the drill string to change the bottomhole assembly (BHA).Since the formation is allowed to flow during UBD operations a surface pressure is ever present in the annulus which is controlled by a rotating control head.Once tripping begins and the pipe is being stripped through the wellhead, this pressure must be handled in some manner before a "pipe light" situation is reached.

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractWellbore pressure management is a critical part of normal drilling practices, where static and dynamic fluid pressures are used to contain formation pressures and to assure wellbore stability. Excessive fluid pressure while circulating can create problems including reduced operating margins between fracture and pore pressures and, in the extreme, lost circulation.To address these problems, an Equivalent Circulation Density (ECD) Reduction Tool (RT) has been developed.The ECD RT is designed to counter the frictional pressure effects that exist while circulating. The tool is expected to have a broad range of drilling applications including the narrow pore/fracture pressure margin deepwater environment, wellbores prone to instability, pressure depleted reservoirs and extended reach wells.The tool has the potential to:• Improve wellbore stability.• Extend hole intervals and reduce casing requirements.• Improve rate of penetration (ROP).• Reduce lost circulation.• Reduce differential sticking.• Improve hole cleaning in extended-reach drilling (ERD) wells through the use of higher flow rates.This paper describes a new downhole tool for ECD reduction, which is run as an integral part of the drill string. A prototype tool has been built, to operate inside 10-3/4" to 13-3/8" casing strings, which has undergone testing in a flow loop and in two experimental wells. The design features of this prototype and the test results obtained so far are discussed in this paper.

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fax 01-972-952-9435. AbstractWellbore pressure management is a critical part of the drilling process. In normal drilling practices, static and dynamic fluid pressures are used to contain formation pressures and to assure wellbore stability. Excessive fluid pressure while circulating can create problems including reduced operating margins between fracture and pore pressures and, in the extreme, lost circulation.To address these problems, an Equivalent Circulation Density (ECD) Reduction Tool (RT) has been developed.The ECD RT is designed to counter the frictional pressure effects that exist while circulating. The tool is expected to have a broad range of drilling applications including; the narrow pore/fracture pressure margin deepwater environment, wellbores prone to instability, pressure depleted reservoirs, and extended reach wells.The tool has the potential to:• Improve wellbore stability • Extend hole intervals and reduce casing requirements • Improve well control • Reduce lost circulation • Reduce differential sticking • Improve hole cleaning in ERD wells through the use of higher flow rates This paper describes a new downhole tool for ECD reduction, which is run as an integral part of the drill string. A prototype tool has been built to operate inside 10-3/4" to 13-3/8" casing. This tool has undergone laboratory testing and full-scale technology trials are in progress. The design features of this prototype are discussed along with the laboratory test results obtained to date.