Productivity Impairment of Openhole Gravel Packs Caused by Drilling-Fluid Filtercake

Abstract

Abstract One of the many benefits of installing open-hole completions in high angle or horizontal wells is higher well productivity compared to cased and perforated completions. This is particularly true in applications requiring down-hole sand retention. However, earlier studies have shown that productivity of open-hole completions can be impaired by drilling fluid filtercake or filtercake residue. Unfortunately, to obtain a complete gravel pack in an open-hole section, it is necessary to leave the filtercake intact. Once the gravel is placed, this filtercake becomes trapped between the borehole wall and the gravel pack. The final disposition of this filtercake layer has been the source of much speculation over the past 10 - 15 years. Many proponents of open-hole gravel packing contend the filtercake ultimately disperses into discrete components and passes through the gravel pack and screen without impairing productivity. Others suggest that the filtercake is more tenacious and is breached in random, limited locations along the length of the completion leaving the majority of the filtercake intact. If the filtercake is not effectively removed and inflow area is significantly reduced, areas of concentrated flow commonly referred to as "hot-spots" can be created leading to impaired productivity and/or completion failure. This paper presents a laboratory investigation of open-hole gravel pack impairment from drilling fluid filtercake conducted under simulated down-hole conditions. A limited number of commonly-used Drill-in Fluid (DIF) formulations were selected for this study along with unconsolidated, formation sand samples obtained from whole core. Gravel sizes used in the study were based on the median grain size of the formation sand and ranged from conservatively sized (D50/d50 ~ 2.0) to aggressively sized (D50/d50 > 8). Results of the tests show the extent of filtercake damage to both the formation sand and the gravel pack as well as the depth of permeability reduction. Finally, the benefit of placing a remedial treatment in the open-hole section following the gravel pack is discussed.