The Mississippi Fan is a broad, arcuate accumulation of Pleistocene deep-water sediments deposited in the eastern Gulf of Mexico. Multiple acoustical sub-bottom reflectors can be traced regionally across the entire fan, dividing this sediment body into sediment packages called fan lobes. Seven of these acoustical reflectors have been mapped and they divide the fan into seven fan lobes. Structure and isopach maps of these fan lobes reveal a general shift during the Pleistocene from west to east and toward deeper water. Each fan lobe is basically a channel-overbank complex with differing morphology and channel characteristics that allow it to be divided into upper, middle, and lower fan physiographic regions.The upper fan region of the modern fan lobe connects to the Mississippi Canyon and is characterized by a nearly filled, large erosional channel with broad levees. A smaller, central channel is cut into the large channel fill.The middle fan region starts near the major break in slope. It is convex in cross section with a sinuous channel at its apex. The size of the channel as well as its sinuosity decrease downfan. An acoustical high-amplitude zone near the base of the channel fill coincides with coarse-grained material.The lower fan region starts where the single sinuous channel pattern changes into a set of near-parallel surface images, interpreted to be former channel courses. Only one channel was active at a given time and its life span was geologically short before it shifted to a new position. At the distal end, these channels may bifurcate before becoming unrecognizable on high-resolution seismic records and sediment deposition changes from a confined to an unconfined mode. The latter is characterized by sheet-sand deposition containing a significant amount of sand that originated from upper slope and shelf environments.Major objectives for drilling the Mississippi Fan were to place the fan lobes into a time-stratigraphic framework, to determine if the midfan channel is migratory in nature, to establish the lithological characteristics of the acoustical high-amplitude zone present near the bottom of the channel fill, to analyze if sand is transported to the lower fan and in which depositional mode it is emplaced, to confirm or modify existing fan models, and to determine the physical and chemical characteristics of these deep-sea fan deposits.Nine sites were occupied on the Mississippi Fan, four (Sites 621, 622, 617, and 620) on the middle fan, four (Sites 623, 624, 615, and 614) on the lower fan, and one (Site 616) on the flank of the youngest fan lobe and within a surface slump deposit. Most of the holes penetrated only the youngest fan lobe.In addition to these nine sites, two sites (618 and 619) were occupied on the continental slope off Louisiana in intraslope basins formed as the result of active salt diapirism. Orca Basin (Site 618), characterized by a 200-m-thick anoxic, high salinity layer of bottom water, was expected to provide a complete upper Neogene stratigraphical and chemical record. Howev...

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Lost circulation is one of the main causes of nonproductive time during drilling and impacts the success of cementing operations. Losses into the reservoir not only impact drilling, they potentially impact the reservoir, due to influx of quantities of drilling fluids that are potentially damaging, or will influence the production rate. Existing solutions are based mainly on particulates, which often are added to drilling fluids to plug fractures or to build up filtercake to cure fluid losses. When particulates are applied for curing losses in reservoir sections, it is desirable that the plugging materials maintain stability for sufficient time to allow well completion but eventually self-degrade to leave undamaged formation for future hydrocarbon production. The main challenges are the design of the lost-circulation material to cure losses into fractures of various widths and to provide plug stability and cleanup within a desired time frame over a broad bottomhole temperature range.Fibers have shown good fracture-plugging behavior. Parameters affecting fiber performance include, but are not limited to, fluid viscosity, fiber concentration, fiber geometry, flow rate, effect of the wall, and fracture width. To effectively apply fibers as lost-circulation applications, a novel, fiber-laden fluid was designed for easy preparation on surface, allowing compatibility with bottomhole assemblies (BHAs). The decrease in velocity inside the fracture enables fibers to bridge and then plug the fracture, thus regaining circulation. The fibers are specially designed to degrade in an adjustable time frame sufficient to ensure plug stability until the well is completed. With time, the plug undergoes further degradation, leading to nondamaged formation for production.This novel degradable solution has been successfully proven during field trials in various drilling scenarios ranging from severe to total losses with effective and efficient loss mitigation, without issues on placement through BHA and bit nozzles, and mitigating further reservoir damage.

Loss circulation is the biggest challenge after drilling and weather-related problems during the process of constructing new wellbores. As per industry figures, more than USD 2 billion per year are spent in combating losses. In the Kohat-Potwar plateau of the Upper Indus basin of northern Pakistan, a harsh and complex environment, a well usually takes anywhere from 180 to 270 days to drill. The overall time taken to drill depends on the formation thicknesses, severity of the losses, and the concession location within northern Pakistan. High-pressure water zones are located close to salt and shale formations, above the potential reservoirs. While drilling through the high-pressure formations, high mud weights greater than 1980 kg/m3 (16.5 lbm/gal) are required to maintain a well under control, which often leads to induced losses during drilling and also while running casing. The mud weight is typically lowered to 1500 kg/m3 (12.5 lbm/gal) or lighter to combat massive losses in naturally fractured limestone formations in the production hole. Engineered fiber-based loss circulation (EFBLC) control pills, based on a specially engineered fiber system and the particle size distribution principle, were developed to control the losses. The pills were effective in curing losses during drilling and while cementing; prior to the introduction of the EFBLC pills, operators spent days in combating losses with numerous traditional methods. Also, the pills were robust enough to work in water-base mud (WBM), oil-base mud (OBM), or synthetic-base mud (SBM) environments with weights up to 2040 kg/m3 (17.0 lbm/gal). In applications in northern Pakistan, the EFBLC pills were successful in combating the losses while drilling and cementing, thus reducing the threat of nonproductive time (NPT);minimizing the quality, health, safety and environmental (QHSE) concerns of well control; and preventing costly remedial jobs due to poor zonal isolation.