Formation damage minimization and removal are important factors in enhancing field productivity and achieving targeted production rate. While formation damage is anticipated during drilling, an effective wellbore cleanup fluid becomes essential to remove mud damage and enhance well productivity. Filter cake layer created by drilling fluid can impair production considerably and should be removed prior to production using an effective treatment. Filter cake can be removed using a chemically designed filter cake removal treatment. The design of the treatment requires considerations of mud type and reservoir conditions. Also, it is important to consider the compatibility aspect of the treatment fluid with formation fluids and drill-in fluid base oil. Incompatible fluids result in precipitation which leads to further formation damage. In Saudi Arabia, many sandstone reservoirs are drilled with invert emulsion drill-in fluid to avoid the risk of clays swelling, which can lead to hole sloughing and formation damage. However, production impairment due to mud damage effect was observed in some horizontal wells drilled with invert emulsion drill-in fluid and completed with stand-alone screens as a result of improper mud managemet. After being put on production, their production rates have been reduced significantly with time. The decrease in production was related to screen blockage and mud cake impairment. A newly developed single-stage treatment was spotted and soaked to remove oil based mud cake and screen blockage. A significant sustained improvement in production was noticed and flowback solids indicated removal of screen blockage and mud cake. Lab studies were conducted at reservoir simulated conditions to evaluate the effectiveness of the treatment. The study covered testing the treatment filter cake removal efficiency, return permeability tests with reservoir core samples, and compatibility tests with formation fluids and drill-in fluid base oil. This paper will discuss in detail the laboratory work conducted and the successful field treatment performed.
Expandable sand screens are a globally accepted sand control system with more than 600 installations worldwide across all vendors. A growing body of data suggests that when compliantly expanded in openhole they perform very well, with consistently low skins and high PIs. Where comparisons have been done, the expandable screens perform at least as well as other sand exclusion systems such as standalone screens and openhole gravel packs. There are a number of possible reasons for the high performance:1) The ESS presents a large open area to the formation. This gives a low pressure drop across the screen and minimizes the possibility of plugging to a minimum. 2) The compliant expansion into contact with the wellbore limits the zone of deformation around the hole. 3) Compliance also improves filter cake clean up by reducing mixing with failed sand.The effect of compliance has been investigated in two sets of experiments. The first was full scale test with a compliant expandable screen and a stand alone screen with an annulus. The expandable showed 60% higher productivity than the screen with an annulus. The second set of experiments was in a specially designed Perspex cell. This cell allowed the effect of an annulus to be investigated for a variety of different sands from well sorted to poorly sorted. The results show that the compliant screen has advantages in sand retention and 100% greater productivity.Taken as a whole, the field results and the two types of experiment show in a very clear way the benefits on productivity of compliant sand screens. * Now with Chevron 1 ESS is a registered trademark of Weatherford to isolate using conventional mechanical techniques and ability to subsequently isolate sources of unwanted water production.
Targeting thin sand bodies while drilling across heterogeneous sandstone reservoir is a major challenge that requires integrated reservoir engineering, formation evaluation, geological and geophysical contributions. The objective of this paper is to exemplify geosteering challenges when drilling horizontal power water injector across Permian eolian sandstone reservoirs with high degree of structural and reservoir uncertainty. The integrated reservoir management team has utilized the geological and seismic impedance to locate a power water injector in the southwestern flank of the field to support pressures during production from offset wells. Seismic impedance indicated that the target area comprises of beds with high degree of lateral and vertical heterogeneity. The team decided first to drill the well utilizing a conventional logging while drilling (LWD) tool to geosteer the well in the horizontal section. The LWD was unable to trace the sand while drilling across the heterogeneous sandstone reservoir. The team decided to abandon the hole and sidetrack the well with a new lateral, utilizing directional and deep resistivity (DDR) while drilling to improve geosteering and optimizing of well placement. The DDR measurements provide remote detection of bed boundaries around the wellbore. This technique has been used successfully in other analogous sandstone reservoirs of Saudi Arabia to ensure maximum reservoir contact. The results of using this approach were very encouraging and a net to gross of 62% was achieved. It can be concluded from the results that the DDR technology is an effective way to efficiently drill and place water injector wells. It has the potential to reduce the number of injector wells drilled, thus cutting cost and meeting the production goals. Introduction Eolian and fluvial channel sand deposits are significant petroleum exploration targets in many basins around the world. The quality of sand and stratigraphic hydrocarbon trapping mechanism plays an important role to the type of wells drilled to produce the hydrocarbons. Power water injector wells are drilled to maintain pressure and improve oil recovery. The success of the water injector depends on how effectively the wells are placed relative to reservoir quality, flow direction and structure. Therefore it is essential to characterize the eolian and fluvial channel sand depositional system.
Fluids identification in reservoirs that bear low or mixed formation water salinity poses a challenge for reservoir management in terms optimum well placement strategies and reservoir surveillance. The logging industry provides many technologies to help characterize in-situ fluids while drilling or during the production stage. An integrated reservoir engineering team has established an integrated formation evaluation methodology to identify fluids encountered in the reservoir, while drilling or while monitoring saturation changes periodically in key observation wells. A number of new and re-entry wells were selected to measure fluid saturation while drilling via different saturation tools; namely, resistivity, nuclear magnetic resonance (NMR), formation pressure testing and fluid sampling, and advanced mud gas logging to complement each other. Carbon/oxygen (C/O), coupled with a flowmeter survey, were run in two observation wells, in both flowing and shut-in conditions, and showed positive results for enhacing the capability to monitor saturation. Following a comprehensive evaluation of all acquired data and interpretation, the petrophysical model was calibrated using NMR and downhole fluid samplings. Results have enabled building fluid characterization criteria for low contrast salinity clastic rocks based on reservoir complexity and fluid uncertainty. The optimized C/O acquisition helped with analyzing fluid saturations and building an intriguing process to address challenges related to different environmental conditions. This evolved methodology revealed a more consistent saturation mapping with the actual reservoir understanding while identifying the optimum completion and excellent wellbore conditions for such a method. The established fluid identification process, while drilling, will help optimizing well placement and well completion to yield productive wells. The customized C/O log process will enhance reservoir surveillance and monitor saturation change to assess sweep efficiency and overall field performance.
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