**4. Methodology**

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

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

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

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

which increases plastic viscosity and decreases drilling performance [8].

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

92 Drilling

be removed [12].

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

ROP which is directly related to ECD [5].

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

#### **4.1. Setup of solid control system**

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

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

redistribute the mud through lines to respective shale shakers is designed to optimize the mud flow performance. This improvement minimized the tendency of shale shakers overflow and reduced processing overloading (**Figure 5**).

**5.1. Performance of solid control system on plastic viscosity**

sure loss and inconsistent mud flow.

**Figure 7.** YP (lbs/100 ft<sup>2</sup>

**5.2. Performance of solid control system on yield point**

**Figure 6** shows the tabulated PV of new design and old design solid control system. At the start of drilling operation, PV for both systems performed on the same trend. This reflects the solid separation and treatment was working effectively. As drilling deeper at Well A with old system and more drilled cuttings excavated, the mud viscosity was getting thicker that resulted the PV to gradually increase. Increase of PV is subjected to drilling the Well B with new system design had improved the solid removal processing by 14% as compared to old design. The performance of new system was economical and reliable as system capability justifies it to maintain the PV reading throughout the operation. The inability of the old design to eliminate rapid development of mud contamination significantly leads to overloading works at downstream equipment which increase solid contents in the drilling mud. Frequent mesh screen plugging, discharge rope from the hydrocyclone and solid recirculation contributed to poor solid removal and PV increment. Spray discharge was not achieved because the old design utilized high pressure hose as a suction line to desander and desilter. Pressure generated to feed the mud into desander and desilter through suction hose caused vibration, pres-

Solid Control System for Maximizing Drilling http://dx.doi.org/10.5772/intechopen.76149 95

**Figure 7** shows the tabulated YP for old design and new design. The YP of old design gradually increased because solid in the drilling mud was not properly discarded while drilling well A. Mud overflow on the shale shakers was frequently observed, and occasionally the

) vs. data point. (Note: Based on personal experience).

#### **4.2. Data acquisition and measurement**

Data collection and evaluation of the mud properties include PV, YP and LGS. These measures are used as a tool to evaluate the efficiency of the mechanical equipment. The drilling parameters including ECD and ROP are obtained from real-time downhole acquisition tool. Drill string drag is recorded after each drill pipe connection to monitor the hole condition. Mud parameters and drilling data are correlated to oversee the drilling performance. Gradual changes in mud properties such as high ECD and poor ROP are significantly reflect to the ineffective of solid control system.

## **5. Results and discussion**

Field data are obtained from onshore drilling in Borneo Block. All data are obtained from two different wells with similar lithology called Well A and Well B. The Well A was drilled using original solid control system while Well B was drilled with New developed design. The performance of both systems was compared while drilling the 12.25 inch section. A total of 40 mud samples were collected and measured to evaluate the PV, YP and LGS. These results act as a preliminary step to investigate the performance of the mud on ROP, ECD and drill string drag to justify the performance of the new design in this analysis.

**Figure 6.** YP (lbs/100 ft<sup>2</sup> ) vs. data point. (Note: Based on personal experience).

### **5.1. Performance of solid control system on plastic viscosity**

redistribute the mud through lines to respective shale shakers is designed to optimize the mud flow performance. This improvement minimized the tendency of shale shakers over-

Data collection and evaluation of the mud properties include PV, YP and LGS. These measures are used as a tool to evaluate the efficiency of the mechanical equipment. The drilling parameters including ECD and ROP are obtained from real-time downhole acquisition tool. Drill string drag is recorded after each drill pipe connection to monitor the hole condition. Mud parameters and drilling data are correlated to oversee the drilling performance. Gradual changes in mud properties such as high ECD and poor ROP are significantly reflect to the

Field data are obtained from onshore drilling in Borneo Block. All data are obtained from two different wells with similar lithology called Well A and Well B. The Well A was drilled using original solid control system while Well B was drilled with New developed design. The performance of both systems was compared while drilling the 12.25 inch section. A total of 40 mud samples were collected and measured to evaluate the PV, YP and LGS. These results act as a preliminary step to investigate the performance of the mud on ROP, ECD and drill string drag

flow and reduced processing overloading (**Figure 5**).

to justify the performance of the new design in this analysis.

) vs. data point. (Note: Based on personal experience).

**4.2. Data acquisition and measurement**

94 Drilling

ineffective of solid control system.

**5. Results and discussion**

**Figure 6.** YP (lbs/100 ft<sup>2</sup>

**Figure 6** shows the tabulated PV of new design and old design solid control system. At the start of drilling operation, PV for both systems performed on the same trend. This reflects the solid separation and treatment was working effectively. As drilling deeper at Well A with old system and more drilled cuttings excavated, the mud viscosity was getting thicker that resulted the PV to gradually increase. Increase of PV is subjected to drilling the Well B with new system design had improved the solid removal processing by 14% as compared to old design. The performance of new system was economical and reliable as system capability justifies it to maintain the PV reading throughout the operation. The inability of the old design to eliminate rapid development of mud contamination significantly leads to overloading works at downstream equipment which increase solid contents in the drilling mud. Frequent mesh screen plugging, discharge rope from the hydrocyclone and solid recirculation contributed to poor solid removal and PV increment. Spray discharge was not achieved because the old design utilized high pressure hose as a suction line to desander and desilter. Pressure generated to feed the mud into desander and desilter through suction hose caused vibration, pressure loss and inconsistent mud flow.

#### **5.2. Performance of solid control system on yield point**

**Figure 7** shows the tabulated YP for old design and new design. The YP of old design gradually increased because solid in the drilling mud was not properly discarded while drilling well A. Mud overflow on the shale shakers was frequently observed, and occasionally the

**Figure 7.** YP (lbs/100 ft<sup>2</sup> ) vs. data point. (Note: Based on personal experience).

unit was bypassed to minimize the surface losses. By passing the solid control unit significantly overload the downstream mechanical equipment and result the equipment incapable to remove the solid efficiently. Changes in low shear rate viscosity reflect to the mud YP. In this condition, colloidal clay platelets link together (flocculate) with consequent increase in their specific surface area. When mud is at static condition, the mud contains high solid and becomes attractive and repulsive. Stable and consistent mud flow distribution to shale shakers was helpful in controlling the YP build up. The ability of the new design to maintain the YP showed that the solids were properly separates by the system and result in low pressure loss while the drilling mud was circulated. Consistent value of YP at new design while drilling the section typically provides good cutting carrying capacity (CCC) of the drilling fluid. Good control of YP reduces the chances of pressure spike that can break the formation which may result circulation lost. Sufficient YP and gel strength were achieved at acceptable gel strength to help for cutting suspension while circulating and pump shutdown. Moreover, the mud was capable to lift the cuttings from bottom of the hole to surface.

return from the well. Frequent shale shakers overflow and bypassing the shakers in order to prevent massive surface loss of expensive fluids significantly created additional risk to the solid removal processing. The situation results of the LGS in the mud system rapidly increased to 14%. High solid content in this mud was considerably abrasive and may degrade down the drilling equipment through silt size. The smaller the particles, the more pronounced the effect on the mud properties because smaller particles are more difficult to remove or control its effect on the fluid. Recirculating of mud that contained drilled solid may gradually deteriorate mud properties. The upper limit of the solid fraction should be in the range of 6–8% by volume. The new design of solid control system as tabulated in **Figure 8** shows that the system LGS was improved with system removal by 25% when drilling Well B which showed an average reading of LGS at 8.7%.

Solid Control System for Maximizing Drilling http://dx.doi.org/10.5772/intechopen.76149 97

**5.4. Performance of solid control system on mud weight and equivalent circulating** 

Well A was drilled using old design solid control system. The section was from 760 to 2163 m MDRT. MW was gradually increased from 10 to 11.6 ppg mud to maintain the hydrostatic

**density**

**Figure 9.** Section depth vs. MW & ECD (new design).

#### **5.3. Performance of solid control system on low-gravity solid**

**Figure 8** shows the tabulated LGS for old design and new design. Rapid increment of LGS while drilling Well A was obvious due to inability of the old design to remove the solid efficiently from drilling mud. At the start of drilling operation, both designs removed the solid effectively from the drilling mud as the LGS was tabulated at the range of 7–8%. As drilling Well A deeper, the solid control equipment (SCE) of old design was observed getting poor in handling the mud

**Figure 8.** LGS (%) vs. data point. (Note: Based on personal experience).

return from the well. Frequent shale shakers overflow and bypassing the shakers in order to prevent massive surface loss of expensive fluids significantly created additional risk to the solid removal processing. The situation results of the LGS in the mud system rapidly increased to 14%. High solid content in this mud was considerably abrasive and may degrade down the drilling equipment through silt size. The smaller the particles, the more pronounced the effect on the mud properties because smaller particles are more difficult to remove or control its effect on the fluid. Recirculating of mud that contained drilled solid may gradually deteriorate mud properties. The upper limit of the solid fraction should be in the range of 6–8% by volume. The new design of solid control system as tabulated in **Figure 8** shows that the system LGS was improved with system removal by 25% when drilling Well B which showed an average reading of LGS at 8.7%.

## **5.4. Performance of solid control system on mud weight and equivalent circulating density**

Well A was drilled using old design solid control system. The section was from 760 to 2163 m MDRT. MW was gradually increased from 10 to 11.6 ppg mud to maintain the hydrostatic

**Figure 9.** Section depth vs. MW & ECD (new design).

unit was bypassed to minimize the surface losses. By passing the solid control unit significantly overload the downstream mechanical equipment and result the equipment incapable to remove the solid efficiently. Changes in low shear rate viscosity reflect to the mud YP. In this condition, colloidal clay platelets link together (flocculate) with consequent increase in their specific surface area. When mud is at static condition, the mud contains high solid and becomes attractive and repulsive. Stable and consistent mud flow distribution to shale shakers was helpful in controlling the YP build up. The ability of the new design to maintain the YP showed that the solids were properly separates by the system and result in low pressure loss while the drilling mud was circulated. Consistent value of YP at new design while drilling the section typically provides good cutting carrying capacity (CCC) of the drilling fluid. Good control of YP reduces the chances of pressure spike that can break the formation which may result circulation lost. Sufficient YP and gel strength were achieved at acceptable gel strength to help for cutting suspension while circulating and pump shutdown. Moreover, the

**Figure 8** shows the tabulated LGS for old design and new design. Rapid increment of LGS while drilling Well A was obvious due to inability of the old design to remove the solid efficiently from drilling mud. At the start of drilling operation, both designs removed the solid effectively from the drilling mud as the LGS was tabulated at the range of 7–8%. As drilling Well A deeper, the solid control equipment (SCE) of old design was observed getting poor in handling the mud

mud was capable to lift the cuttings from bottom of the hole to surface.

**5.3. Performance of solid control system on low-gravity solid**

96 Drilling

**Figure 8.** LGS (%) vs. data point. (Note: Based on personal experience).

pressure in the column. Early tabulated data on the top section demonstrated a good ECD trend with no significant pressure spike. As drilling reached to 1124 m MDRT depth, ECD spike was increased up to 12.4 ppg. Failures to transport the cutting effectively to surface exposed the formation to pressure spike. It occurred because drilled cutting that remains in the well created tight tolerances between hole and drill string geometries. Poor hole cleaning triggered high ECD that can break the formation and losses of mud. ECD trend progressively built up, and pressure spike was observed at 1244 and 1474 m MDRT. Well circulation was commenced until the hole clean, but the entire operation progress became slows. The flow rate was ramped up in controlled manner to minimize the risk of pressure spike and high ECD. The ROP was also controlled to reduce the impact of high ECD. The average ECD additive factor was 0.6 ppg that is equivalent to 4.9% increment from original MW during mud than in dynamic condition (**Figures 9** and **10**).

gravity effect at deviated hole, heavier cuttings and mud along the lower side of the hole moved at lower rate than the clean mud on the upper side. Peak performance of solid separation equipment is essentially important to ensure the LGS, YP and PV are maintained within the acceptable envelope. These parameters provide good cutting transport and no excessive pumping pressure required to break the gel. The average ECD additive factor was 0.3 ppg that is equivalent to 2.9% increment from original MW during mud flow in dynamic condition.

Solid Control System for Maximizing Drilling http://dx.doi.org/10.5772/intechopen.76149 99

The ROP trend of old design was seen concentrated at range between 40 and 60 m/h. ROP was controlled in such manner due to ECD surge. Mud properties specification was not within the recommended limit, and it significantly influenced the ROP consistency. Continuous of solid built up in the mud system altered the mud properties which eventually causing in poor drilling performance. Drilled solids circulated up the annulus increased the pressure differential and lead to slower drilling. Instantaneous maximum ROP achieved using old design SCE was 62 m/h with 48.78 m/h on average. Drilling the same section for Well B using new design solid control system showed improvement on ROP trend. Maximum instantaneous ROP was registered at 77 m/h with 61 m/h in average. Efficient solid removal using new design improved

Drag force is known as difference between free rotating weight and the force required to move the string up and down in the hole. Pick-up (P/U) drag force usually higher than the free rotating weight while slack-off (S/O) force is lower than the free rotating weight. String weight or

**5.5. Performance of solid control system on rate penetration**

**5.6. Performance of old design of solid control system on hooks load**

the ROP performance by 25% (**Figure 11**).

**Figure 11.** Section depth vs. ROP.

Well B was drilled using new design of solid control system. The section was drilled from 750 to 2200 m MDRT. The MW used to drill this section was 10.0 to 11.9 ppg and gradually increased to maintain the hydrostatic pressure in the column. The tabulated data show that the ECD was consistent at safe drilling margin until section TD at 2150 m MDRT. No significant ECD spike was observed throughout the operation. A slight increase was observed at 1935 m MDRT with 12.32 to 12.5 ppg, but the impact is still below the fracture gradient. Increase in ECD occurred because more cutting bed accumulated on the low side of drill string. Due to

**Figure 10.** Section depth vs. MW & ECD (old design).

gravity effect at deviated hole, heavier cuttings and mud along the lower side of the hole moved at lower rate than the clean mud on the upper side. Peak performance of solid separation equipment is essentially important to ensure the LGS, YP and PV are maintained within the acceptable envelope. These parameters provide good cutting transport and no excessive pumping pressure required to break the gel. The average ECD additive factor was 0.3 ppg that is equivalent to 2.9% increment from original MW during mud flow in dynamic condition.

#### **5.5. Performance of solid control system on rate penetration**

The ROP trend of old design was seen concentrated at range between 40 and 60 m/h. ROP was controlled in such manner due to ECD surge. Mud properties specification was not within the recommended limit, and it significantly influenced the ROP consistency. Continuous of solid built up in the mud system altered the mud properties which eventually causing in poor drilling performance. Drilled solids circulated up the annulus increased the pressure differential and lead to slower drilling. Instantaneous maximum ROP achieved using old design SCE was 62 m/h with 48.78 m/h on average. Drilling the same section for Well B using new design solid control system showed improvement on ROP trend. Maximum instantaneous ROP was registered at 77 m/h with 61 m/h in average. Efficient solid removal using new design improved the ROP performance by 25% (**Figure 11**).

#### **5.6. Performance of old design of solid control system on hooks load**

Drag force is known as difference between free rotating weight and the force required to move the string up and down in the hole. Pick-up (P/U) drag force usually higher than the free rotating weight while slack-off (S/O) force is lower than the free rotating weight. String weight or

**Figure 11.** Section depth vs. ROP.

**Figure 10.** Section depth vs. MW & ECD (old design).

than in dynamic condition (**Figures 9** and **10**).

98 Drilling

pressure in the column. Early tabulated data on the top section demonstrated a good ECD trend with no significant pressure spike. As drilling reached to 1124 m MDRT depth, ECD spike was increased up to 12.4 ppg. Failures to transport the cutting effectively to surface exposed the formation to pressure spike. It occurred because drilled cutting that remains in the well created tight tolerances between hole and drill string geometries. Poor hole cleaning triggered high ECD that can break the formation and losses of mud. ECD trend progressively built up, and pressure spike was observed at 1244 and 1474 m MDRT. Well circulation was commenced until the hole clean, but the entire operation progress became slows. The flow rate was ramped up in controlled manner to minimize the risk of pressure spike and high ECD. The ROP was also controlled to reduce the impact of high ECD. The average ECD additive factor was 0.6 ppg that is equivalent to 4.9% increment from original MW during mud

Well B was drilled using new design of solid control system. The section was drilled from 750 to 2200 m MDRT. The MW used to drill this section was 10.0 to 11.9 ppg and gradually increased to maintain the hydrostatic pressure in the column. The tabulated data show that the ECD was consistent at safe drilling margin until section TD at 2150 m MDRT. No significant ECD spike was observed throughout the operation. A slight increase was observed at 1935 m MDRT with 12.32 to 12.5 ppg, but the impact is still below the fracture gradient. Increase in ECD occurred because more cutting bed accumulated on the low side of drill string. Due to free rotating weight on this analysis represented by the green curve. Data were taken while the string was off bottom to compare0 the modeling string weight and actual weight. As designed expectation, the plots should tabulate across and along the modeling string weight at any well depth. Drilling the Well A using old design system, more solids were not properly separated from the mud. This increased the mud viscosity and altered the mud properties. In this chart, the hook load readings when P/U the drill string was tabulated between 0.2 and 0.3 FF as shown in **Figure 12**. Occasionally, the plot exceeded that friction factor line as observed at depth around 1550 and 1900 m MDRT. Pile up of drilled cuttings bed and accumulation increased the drill string contact with the wellbore. Mud circulation for hole cleaning was performed to remove the cuttings from the well. S/O weight of the drill string in this chart was observed between 0.2 and 0.3 FF. The plots were occasionally tabulated exceeding the 0.3 FF. This condition indicated that more drilled cutting was still sticking and restricting

the drill string to move down. It required extra cumulative axial force to free the drill string. Lower S/O FF represents high hook load and vice versa. Failure to effectively transport the cuttings to surface result in a number of drilling problems including: excessive overpull on trips, high rotary torque, stuck pipe, hole-pack off, excessive ECDs and cutting accumulation.

Solid Control System for Maximizing Drilling http://dx.doi.org/10.5772/intechopen.76149 101

The new design system effectively separated the drilled cuttings from the mud and allowed each of the equipment to work at peak performance. Mud properties were within the design specification with no severe solid contamination result improvement on PV, YP and LGS reading.

**5.7. Performance of new design of solid control system on hook load**

**Figure 13.** Hook load effect vs. depth (new design).

**Figure 12.** Hook load effect vs. depth (old design).

the drill string to move down. It required extra cumulative axial force to free the drill string. Lower S/O FF represents high hook load and vice versa. Failure to effectively transport the cuttings to surface result in a number of drilling problems including: excessive overpull on trips, high rotary torque, stuck pipe, hole-pack off, excessive ECDs and cutting accumulation.

### **5.7. Performance of new design of solid control system on hook load**

The new design system effectively separated the drilled cuttings from the mud and allowed each of the equipment to work at peak performance. Mud properties were within the design specification with no severe solid contamination result improvement on PV, YP and LGS reading.

**Figure 13.** Hook load effect vs. depth (new design).

**Figure 12.** Hook load effect vs. depth (old design).

free rotating weight on this analysis represented by the green curve. Data were taken while the string was off bottom to compare0 the modeling string weight and actual weight. As designed expectation, the plots should tabulate across and along the modeling string weight at any well depth. Drilling the Well A using old design system, more solids were not properly separated from the mud. This increased the mud viscosity and altered the mud properties. In this chart, the hook load readings when P/U the drill string was tabulated between 0.2 and 0.3 FF as shown in **Figure 12**. Occasionally, the plot exceeded that friction factor line as observed at depth around 1550 and 1900 m MDRT. Pile up of drilled cuttings bed and accumulation increased the drill string contact with the wellbore. Mud circulation for hole cleaning was performed to remove the cuttings from the well. S/O weight of the drill string in this chart was observed between 0.2 and 0.3 FF. The plots were occasionally tabulated exceeding the 0.3 FF. This condition indicated that more drilled cutting was still sticking and restricting

100 Drilling

The hook load chart indicated that P/U weight was concentrated at 0.2 FF but occasionally exceeded 0.2 FF. Good control of mud return and consistent distribution flow to solid control system allowed effective solid particles separation. S/O weight of the drill string was observed tabulated below the 0.2 FF but occasionally exceeded 0.2 FF. This indication represented that the hole was not piled up with drilled cuttings. Less axial force was required to move the drill string as there was no severe contact of drilled cuttings with the string (**Figure 13**).

SCE solid control equipment

ECD equivalent circulating density

LGS low gravity solid

NPT non-productive time

P/U pick up S/O slack off

**Author details**

**References**

– Elsevier; 2005

2008;**23**:409-414

FF friction factor

Sonny Irawan\* and Imros B. Kinif

\*Address all correspondence to: drsonny\_irawan@utp.edu.my

2015;**2**(9). e-ISSN: 2395 -0056, p-ISSN: 2395-0072

Universiti Teknologi PETRONAS, Seri Iskandar, Perak, Malaysia

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