**3.1. Effect of solid particles on MW**

Density or MW is measured and expressed in pounds per gallons (lb/gal), pound cubic feet (lb/ft<sup>3</sup> ) and grams per cubic centimeter (g/cm<sup>2</sup> ). It is an important property to maintain the well hydrostatic and prevent gas influx migration into the wellbore. Some of weight material such as barite and hematite are added into the mud to increase the mud weight. Mud in the wellbore column must exert a greater pressure than the fluids in porous rocks that are penetrated by the bit. The pressure exerted by the drilling mud at any depth or gradient of pressure is related to its density. Denser or viscous mud may exert excessive pressure to the wellbore and causing loss of circulation.

#### **3.2. Effect of solid particles on well bottom-hole pressure**

High solid content ultimately can increase the density and viscosity of the mud. Hence, it exposes the well to high BHP and mud properties contamination. Moreover, high horse power is also required to break up the gel and pump the mud for circulation. This not only triggers to hydraulic fracturing effect but also induces the tendency of mud losses into the formation. Under the primary well control requirement, the mud density must be formulated to compensate the desire BHP either meet or exceed the pore pressure of the rock formation. Failure to control the build of solid and regrinding the same drilled cutting may increase the mud surface area become very difficult to remove using mechanical solid control equipment. High solids are abrasive and can increase filter cake thickness. The higher of filter cake, the higher chances of drill string to get stuck due to differential sticking effect. Thin and impermeable filter cake is important to reduce contact area across the drill string.

## **3.3. Effect of solid particles on PV**

**3. Development of solid control equipment**

**Figure 3.** Old design solid control system.

90 Drilling

During drilling operation, the circulated mud carries drilled cuttings to surface. These solids are then treated at mechanical solid control system by separating them from the mud according to the particles size. In this chapter, the research focuses on maximizing the efficiency of equipment performance and separation because the old design was inefficient to remove the solid from the mud. The flow line distributor was installed at the end of return line to the

**Figure 4.** New design solid control system. (Note: **Figures 3** and **4** is based on personal experience).

PV is a function of solids concentration, size and shape of the solid particles and viscosity of liquid phase [4]. It is regarded as a guide to solid control for field application [5]. PV is directly proportional to the increasing of solid volume percentage, or if the volume percent remains constant, the size of the particles decreases. Decreasing particle size may increases surface area that leads to fractional drag problem. This plastic viscosity is sensitive to the concentration of solid and depends largely on the bulk volume of solids in the mud [6]. A low PV implies lower ECD exerted at bottom while high PV trigger to an increase of ECD because high pumping pressure is needed to break the gel. YP/PV ratio is a significant indicator of drilling fluid condition, low ratio indicates smaller tendency for gas cutting, swabbing pressure and greater settling velocity of cuttings whereas high ratios indicate coagulation and flocculation [7]. Removal of drilled solids from a drilling fluid will decrease plastic viscosity, and if this solid remains in the fluids, it will grind into smaller and more numerous particles which increases plastic viscosity and decreases drilling performance [8].

density of a moving fluid and slightly more than the static density because of the friction pressure drop in the annulus. ECD depends on the pump rates and fluid viscosity. Therefore, regulation of ECD within limits means keeping viscosity low. The main cause of elevated viscosity is low gravity solid (LGS) increased. Close monitoring on solid control equipment

Solid Control System for Maximizing Drilling http://dx.doi.org/10.5772/intechopen.76149 93

The solids control comprises of three: shale shakers, hydrocyclones (Desander and Desilter), and centrifuge. The introduction of flow distributor tank at the end of the flowline and

must be performed to ensure that LGS are kept to a minimum [14].

**Figure 5.** Flow diagram of the methodology. (Note: Based on personal experience).

**4. Methodology**

**4.1. Setup of solid control system**

## **3.4. Effect of solid particle on YP**

YP is the initial resistance of the fluids to flow caused by the electrochemical forces between the particles. It is also expected to be a function of the solid concentration of the solids and those factors, such as surface charges and potential, which affect the interparticle forces [9]. YP and gel strength should be low enough to allow sand and shale cuttings to settle out and entrained gas to escape, minimize swabbing effect during pulling the string out of hole and permit the circulation to be started at low pump pressure [10]. Efficient elimination of drilled solids right after the fluid leaves the annulus was the best solution to avoid drilling fluidcutting interaction that subsequently can increase the fluid density [11]. A change in the PV of drilling mud can cause small changes in YP. Therefore, it is always important to keep the viscosity of a mud from getting too low. The mud should have minimum viscosity properties to lift the cuttings from bottom of the hole to surface. The mud must capable to keep the weighting material and drilled cuttings in suspension while circulating or stop pumping. Normal reaction in the event of poor cutting transport is to increase the YP of the mud. However, the significant increase in YP may result poor performance of the finest mesh at shaker screen. Changing the mesh screen to a coarser screen decreases the quantity of drilled solid that can be removed [12].

#### **3.5. Effect of solid particle on ROP**

Rheological and filtration properties become difficult to control when the concentration of drilled solid become excessive [1]. High particulate solids in the mud reduce ROP because of increase in mud density and viscosity. The higher the mud density, the greater the differential pressure exerts. ROP decreases when differential pressure increases. Lower mud density may decrease the dynamic chip hold down and permitting faster RPM. Low viscosity mud promotes fast penetration because of good scavenging of drilled cuttings. Despite applying more WOB and RPM can comfortably achieve the desire ROP, but drilling with contaminated mud properties decreases in ROP in a long run. Darley mentioned that low concentration of noncolloidal drilled solid below 4% capable to maintain ROP at high level [3]. Mud properties such as PV and yield stress/gel strength showed that although these properties have effects on ROP, but not very significant, only annular pressure losses seemed to drastically affect the ROP which is directly related to ECD [5].

#### **3.6. Effect of solid particle on drag and ECD**

The fluid rheology plays an important role for solid transport and optimizes the hole cleaning [14]. The best way to pick solid is with a low viscosity fluid in turbulent flow. Hole cleaning can be optimized by the use of drilling mud with low gel strength and with low viscosity within the shear rates exposed to the annular flow [13]. In situations where ECD is not a limiting factor, high viscosity fluids with high YP/PV ratios are preferred. Under situation where ECD is a limiting factor, the use of thin fluids in turbulent flow should be considered. Driller must ensure the ECD as well as its static density is within the safe limit. ECD is the effective density of a moving fluid and slightly more than the static density because of the friction pressure drop in the annulus. ECD depends on the pump rates and fluid viscosity. Therefore, regulation of ECD within limits means keeping viscosity low. The main cause of elevated viscosity is low gravity solid (LGS) increased. Close monitoring on solid control equipment must be performed to ensure that LGS are kept to a minimum [14].
