**2. Solid content and mechanical solid control system**

always perceived as a vital factor affecting the operation efficiency and equipment wear issues. Ineffective solid control system and inadequate understanding of mud properties create additional risk and uncertainties to downhole condition. Drilling the 12.25 hole section using old design solid control system produced unequal distribution of the mud flow over the shakers screen. The mud flow only concentrated at middle shale shaker that connected to flow line while the others shaker received minimal flow. This situation tends to be overloaded only in the middle shale shaker unit. In rig site practice, the shakerman adjusting the baffle plate at possum belly increases the flow. However, it increased mud losses through the solid control unit and continuous plugging of the mesh in the solid control unit. Due to ineffective shale shaker and overflow of mud at possum belly, the flow was bypassed to prevent mud surface losses but it plugged the apex cones of hydrocyclone. By-passed the shale shaker unit result high drilled solids content circulated back and not remove from the system. Mud properties, such as YP, PV and LGS, were studied to investigate the significant effect of poor solid control system processing toward the performance of ROP, ECD and drag. This investigation evaluated the performance of solid control equipment before and after the introduction of mud flow distributor tank for mud return from the well while drilling the 12.25 inch hole. The methods used were gathering from various sources including case study on the rig operation, reports, personnel experience, publication and discussion for drilling the 12.25-inch hole section. The theory and literature review related to solid control system, mud properties and correlation to drilling operation also were studied to gain previous research related to the problem. Solid control system was then redesigned to investigate its affect toward mud properties and operation

88 Drilling

**Figure 1.** Solid control phases diagram. (Note: Personal experience).

The commercial solids (barite) and non-commercial solid (drilled cuttings) are two primary sources of solid particles that exist during drilling. Solid that are concentrated in the mud are classified either based on specific gravity (SG) or density and particle size. Solid SG higher than 4.2 (weight material) are categorized as high-gravity solid (HGS) while solid with SG 1.6 to 2.9 (average 2.6) is categorized as low-gravity solid (LGS) **(Figure 2).**

The solid control system sequence consists of shale shakers, hydrocyclones (desander and desilter) and centrifuge. Each mechanical equipment work independently depends on the solid particles sizes. The equipment is connected in series, and each stage of processing performance is partly dependent upon the previous equipment. By-passing the shaker screen is not recommended because failure to discard the solid particles at the shale shakers unit would overload the downstream equipment. Drilled solids that are not removed during the first circulation through the surface equipment are always subject to mechanical degradation [3]. The smaller the particle, the greater the surface area may develop, and it is causing greater effect to the mud system (**Figures 3** and **4**).

**Figure 2.** Particle diameter [7].

shale shakers and replaced the high-pressure hose to rigid piping system for reducing pressure loss due to vibration. This system allows the solids containing drilling mud to be divided equally between the desire numbers of shale shakers. Mud circulation without any reduction in solid concentration may thicken the fluid viscosity and develops resistance to flow character of the mud. This brings to the changes in its density, rheology and other properties. The utmost advantage is to remove as much solids practically to reduce down time which contributed from plug flow lines, fluid end repair, drill string erosion and re-drilling of solids as

Density or MW is measured and expressed in pounds per gallons (lb/gal), pound cubic feet

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

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 imperme-

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

). It is an important property to maintain the

Solid Control System for Maximizing Drilling http://dx.doi.org/10.5772/intechopen.76149 91

drilling fluid recycles itself through the mud system loop [1].

) and grams per cubic centimeter (g/cm<sup>2</sup>

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

able filter cake is important to reduce contact area across the drill string.

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

wellbore and causing loss of circulation.

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

(lb/ft<sup>3</sup>

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

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