# Drilling Fluid and Cement Slurry Design for Naturally Fractured Reservoirs
## 4 Preventive and Corrective Lost Circulation Measures
### Corrective Measures to Mitigate Lost Circulation during Drilling
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Lost Circulation Materials (LCMs)** & \\ \hline \multicolumn{2}{c}{**Conventional LCM**} & **Specially Designed LCM** \\ \hline \multirow{3}{*}{**Flay LCM**} & \multirow{3}{*}{\begin{tabular}{c} flaked calcium carbonate, mica, \\ cellophane, vermiculite, and cornccos \\ \end{tabular} } & **Cement Plug** \\  & & Ultra-thixotropic and thixotropic cement \\  & & slurries including calcium carbonate, flakes, \\  & & and mica for mechanical bridging. \\ \hline \multirow{3}{*}{**Granular LCM**} & \multirow{3}{*}{\begin{tabular}{c} calcium carbonate, nutshells, gilsonite, \\ graphite, asphalt, perlite, and course \\ bentonite \\ \end{tabular} } & **Polyurethane Grouting** \\  & & Mixtures or solutions that react to produce a \\  & & graphite, asphalt, perlite, and course \\  & & polyurethane that require water to react and \\  & & two component polyturethanes that are mixed \\  & & and react with each other). \\ \hline \multirow{3}{*}{**Fibrous LCM**} & \multirow{3}{*}{\begin{tabular}{c} sawdust, cellulose fibers, shredded paper, \\ mineral fibers, and nylon fibers \\ \end{tabular} } & **Geopolymer-Based Pill** \\  & & Chemically reactive pill based on aqueous \\  & & alkali alumina silicates. \\ \hline \multirow{3}{*}{**Blended LCM**} & \multirow{3}{*}{\begin{tabular}{c} a mixture of two or more types of LCM \\ \end{tabular} } & **Settable Plug** \\  & & A plug is utilized for slurry, which is a gel or \\  & & solidified; keeps fluid at low viscosity and \\  & & reacts at certain bottom hole temperature. \\ \hline \multirow{3}{*}{**Water-/Acid-Soluble LCM**} & \multirow{3}{*}{\begin{tabular}{c} calcium carbonate, fiber, ground marble \\ and salts \\ \end{tabular} } & **Cross-linked Gel** \\  & & A high-viscosity gel formed by the \\  & & development of cross-linked bonds between \\  & & polymer chains making the polymer network. \\ \hline \multirow{3}{*}{**Hydratable/Swellable LCM**} & \multirow{3}{*}{\
\begin{tabular}{c} A mixture of different LCM with a highly \\ reactive polymer \\ \end{tabular} } & **Viscoelastic Surfactant** \\  & & It is made of surfactants that self-assemble into \\  & & worm-like micellar structures that act as \\  & & polymers, raising the viscosity of the mud at \\  & & low shear rates. \\ \hline \multirow{3}{*}{**Nanoparticles LCM**} & \multirow{3}{*}{
\begin{tabular}{c} iron hydroxide, calcium carbonate, and \\ silica nanoparticles \\ \end{tabular} } & **Degradable Fiber Pill** \\  & & A fiber pill maintains stability for required \\  & & time, but eventually self-degrade within \\  & & desired time frame over a broad Bottomhole \\  & & Temperature (BHT) range. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Lost circulation materials (LCMs). during drilling with particulate and/or fibrous material requires a complete engineered approach that includes borehole stability analysis, equivalent circulating density modelling, leak-off flow-path geometry considerations, drilling fluid type, and LCM material selection to help minimize pressure effects on the ECD, on-site monitoring using pressure while drilling, and a timely application of LCM and treatments [3; 4; 8; 53]. The effectiveness of each particulate LCM treatment can be determined by a slot disc test performed in the laboratory. The laboratory testing was conducted with slots which have different fracture widths ranging from 1 to 2 mm [87], 1, 0.5 and 0.2 mm [88], 3 mm [89], 2 mm [90], and 3 mm [91]. The drilling fluids containing lost circulation materials are forced to pass through the selected disc under HPHT conditions, and the tested LCM is evaluated by both the total 30-min fluid loss and the time it takes to plug a slot disc [4]. Particle Size Distribution (PSD) analysis is also used for proper particle size selection based on the pore size or the estimated fracture width [53]. Figure 4 shows an example of quality and appropriate fracture plugging with conventional LCMs.