Management of Formation Damage by Improved Mud Design

Abstract

Minimising filtrate loss into the formation by forming a filter cake with low porosity and permeability near the wellbore region is the key to managing formation damage problem. Visualising and understanding the structure of a filter cake can help formulate a drilling fluid system that provide an effective caking process with reduced water loss. In this study, a technique that identifies the appropriate mud caking process is suggested. It can be applicable to relevant sandstone formations within 2 inches from the wellbore. This identification technique is based on the measurement of filtrate loss, the measurement of the return permeability of cores exposed to selected muds and the visual observation on the micro-level of cake structures of these muds in order to describe them and highlight their merits. A good mud system is the one which have a low filtrate loss, a low return permeability and a filter cake structure close to that of the ideal internal and external filter cake. This study also provides an investigative and comparative look at the internal and external filter cake structures of different muds using the Scanning Electron Microscopy. This technique verified that the glycol and petrofree drilling fluids possess the characteristics and filtration properties of good mud systems. The glycol filter cake structure was superior to those of the solid free /low solid KCl-polymer muds. Scanning Electron Microscopy provided clear and descriptive images of the structures of internal and external filter cakes. Introduction Over the years, numerous published papers investigated the negative effects of drilling fluids on prospective formations, especially the region adjacent to the Wellbore (Jiao and Sharma, 1992; Marx and Rahman, 1984, 1991; Longeron et al, 1995, Krueger, 1986). Although it serves many important purposes, the introduction of drilling fluids into the virgin formation during the drilling process results in the majority of cases in an irreversible permeability impairment leading to low productivity. For safety reasons, most of the wells are drilled overbalanced, and this differential pressure between the wellbore and across a permeable formation leads to filtration of the drilling mud. Solid particles and mud filtrate are lost to the formation, first at a high rate and then at a decreasing rate due to the deposition of the mud solids on the wall of the borehole (filter cake formation process) to a constant value once the mud solids deposition rate is equal to that of the solids re-entrainment in the mud flow (equilibrium condition). P. 203^

Effect of Weak Preformed Particle Gel on Unswept Oil Zones/Areas during Conformance Control Treatments

“…The results indicate that the selected particle gel cannot propagate through the porous media with a permeability of <320 mD. In these cases, deformable particles form an external filter cake and/or the internal filter, 40 as shown in Figure 7. An external filter cake was formed on the core surface (see Figure 7a).…”

Influence of strong preformed particle gels on low permeable formations in mature reservoirs

“…In these cases, as shown in Fig. 10, PPGs were found to form an internal filter cake or an external filter cake (Azizi et al 1997). On the sandstone core surface, an external filter cake was created (Fig.…”

“…Elsharafi and Bai (2012) determined that the best PPG treatments occurred when the PPG could simply penetrate through the high permeable layers without damaging the low permeable formations. Elsharafi and Bai (2015) found that the permeability of the gel pack in the fluid channels depended upon the particle strength, particle size, brine concentration, and the load pressure. The relationship among the cumulative injection volumes against time is needed to determine the damage to low permeable reservoirs (Ershaghi et al 1986;Vetter et al 1987).…”

The Influence of XC-Polymer on Drilling Fluid Filter Cake Properties and Formation Damage

“…Several previous researchers [8][9][10][11][12] features of the ceramic disks which were used have 10 µm mean pore size distribution and permeability of 775 md to stimulate the formation for filtration process at an appropriate temperature and pressure. The porosity of ceramic disk was determined by using the saturated method (the difference in weight of the disk in dried and saturated conditions).…”