Effect of Size and Concentration of a New Developed Natural, Biodegradable and Environmentally Friendly LCM on Fluid Losses Characteristics

Abstract


Introduction
Lost circulation could be defined simply as a loss of the whole or part of the mud into the formation while drilling operations.It is one of the most common problems encountered in drilling.In addition to the waste of mud and materials costs, it wastes time on rig operations (Alkinani et al., 2018;Alhaidari, 2020).The development of materials and techniques for preventing and or treating it will also be needed (Datwani, 2012).Although lost circulation is not new for the petroleum industries but its prevention still a challenge (Shibeeb et al., 2020).A considerable number of materials called, lost circulation materials, have been developed by different service companies and manufacturers in recent years.However, each of the developed lost control materials has its limitations of use (Alhaidari, 2020).
According to Al Maskary et al. (2014), Lost circulation problems costs the petroleum industries around one billion dollars every year.This involves the cost of the mud lost as well as the treatment cost.Due to the high costs of the LCM, the treatment cost only reaches $200 million/year (Ivan et al., 2003).Lecolier et al. (2005) claimed that 20% to 40% of the drilling operation costs will be for the lost circulation problem.In addition to its costly treatment, if the lost circulation is not treated instantly some other problems will be encountered such as formation damage, kick, pipe sticking (Mostafavi Toroqi, 2012).
The lost circulation control techniques are classified into two methods.The first is the use of a settable composition into the thief zone in order to minimize flow and thereby prevent losses.The other method includes introducing of lost circulation materials (LCM), into the mud formula.These LCM could be classified into two categories: conventional LCM and natural biodegradable LCM.Both types will be presented in more details in later sections of this article.The aim of this study is to develop a new natural LCM, evaluate its prevention capability through experiments and present the effects of material sizes and concentration on controlling lost circulation.In general, lost circulation classes are branded based on the rate of loss per time (m 3 /hr) (Alkinani, 2017;Alsaba et al., 2014a).The loss will be called a seepage loss if the fluid loss rate is between 0.5 and 1 cubic meter per hour.This type of loss could be occurred in any type of formation.Meanwhile, the fluid loss rate from 1 to 10 cubic meter per hour, is known as partial losses which may arise in gravel, minor natural horizontal fractures, or induced vertical fractures (Alsaba et al., 2014a).The fluid loss rate of 15 m 2 /h and higher more are considered significant and titled severe losses.The last lost class is called complete or total losses which refers to a non-return of the fluid to the surface, which can occur in long open sections of gravel, big natural horizontal fractures, caverns, linked and interconnected vugs, and extensively opened induced fractures (Alkinani, 2017;Alsaba et al., 2014a).Moreover, Alhaidari (2020) tabulated the classification of drilling fluid loss classes, as shown in Table 1.(Alhaidari, 2020)

Lost Circulation Materials
Each year, hundreds of new materials are introduced by service providers and manufacturers of lost circulation materials (LCM).However, the lost control materials are classified into two groups: conventional LCM and natural LCM.

Conventional lost circulation materials
According to Mansour et al. (2019), materials should have specific qualities, which are briefly addressed in API standards 13B-1 and 13B-2, in order to be used as conventional LCM.Conventional lost circulation materials are categorized as fibrous, flaky, granular, or a combination of the three.The LCM can be useful if the bridge it generates inside the fracture is strong enough to withstand all of the mechanical forces pushing on it (Cook et al., 2012).Particle bridging is described as the accumulation of solids that restricts inflow.There are several jamming or bridging theories available, with the main purpose of predicting bridging time.Fig. 2 shows the four classes of conventional LCM.Since the core of this study is not the conventional lost circulation materials, only a summary of the most commonly used conventional lost control materials will be presented in Table 2.  (Alkinani, 2017) It is vital to note that several parameters affect the performance of an LCM to control mud losses, such as the LCM type, LCM concentration, particle size distribution of the LCM, and the fracture width (Alsaba et al., 2014b;Alsabagh et al., 2015;Nasiri et al., 2018;Sedaghatzadeh et al., 2021).
In spite of continuing efforts to improve the effectiveness of LCMs and better understand the mechanisms involved in their deployment, significant flaws remain.The most important drawback that LCMs currently face is the failure to seal large fractures.According to Alsaba et al. (2014b,c), these huge fracture sizes feature holes that are a few millimeters or greater in width, and LCMs fail to bridge sufficiently to seal them.The second potential drawback is that it does not work in high-pressure and high-temperature (HPHT) conditions; the LCM seal cannot tolerate the high pressures or it melts due to the high temperatures.Third, private conversations with field engineers indicate that if LCMs are not soluble, they may damage production zones and hence decrease productivity, which might be a terrible issue (Mansour et al., 2019).

Natural and biodegradable materials
The worldwide industrial community is moving toward the use of environmentally friendly materials in their operations, replacing products that are harmful to humans, the environment, and marine life (Caenn et al., 2011;Ismail et al., 2021).Fortunately, the oil and gas industries have commenced to respond to this transformation by applying laws mandated by regional and global Environmental Protection Agencies (Caenn et al., 2011;Ramasamy and Amanullah, 2017;Ismail et al., 2021).Apaleke et al. ( 2012) claimed the while designing LCMs, the use of environmentally benign mud and additives must be considered.This goal is achieved by utilizing LCMs that are driven from natural sources such as plants and vegetable tissues (Green, 1984;Sampey, 2006).Numerous factors affect the manufacture of eco-friendly drilling mud, involving the need for a complex mud treatment facility, high initial costs, and a lack of raw materials (Zhao et al., 2009;Abdou and El-Sayed Ahmed, 2011;Ismail et al., 2021).
Several researchers have focused on improving drilling mud qualities using natural ingredients such as coconut shells, rice husk, cocoa bean shells, sugar cane ash, date seed powder, fibers, grass, and a variety of other locally available materials.The application of these natural materials as LCM additives for controlling lost circulation is one of the primary applications of natural materials in drilling processes (Purnomosidi et al., 2021;Ismail et al., 2021).In recent years, several natural environment friendly LCM has been developed in order to reduce the impact of chemical LCM agents (Sampey, 2006;Hossain and Wajheeuddin, 2016).The most common natural and environmentally-friendly materials that are used as LCMs are summarized in Table 3.

Prosopis Farcta (PF)
PF is a common plant germinating in wide range area.It is a below-ground tree.It looks like a shrub with a height of 20-100 cm (in rare cases up to 4 m high).PF is a small, pricking flower and is found in Algeria, Egypt, Tunisia, Iran, Iraq and Kazakhstan (Qasem, 2007).The shrubs grow noticeably in the warm summer months.The mesquite can survive difficult weather and soil conditions (including saline soil), but dislikes shadows (Patil, 2021).The chemical composition of the PF beans has been determined by Omidi et al. (2012) as shown in Table 4.It could be noted for the composition table, that the PF has a fibrous nature which is a type of the most common LCM.Beans of PF were collected from the outskirts of Koya district in Erbil province, Iraq, during the summer of 2021 as shown in Fig. 3.The PF beans then being dried in sun light and then being powdered by griding.Moreover, in order to determine the effect of LCM particle size distribution, the powdered PF beans were divided into three different sizes, fine, medium and coarse through the use of API standard mesh sieves.

Calcium Carbonate (CaCO3)
Almost all of the northern Iraqi fields are suffering from lost circulation, particularly in the reservoir formations.This is because of the highly fractured characterization of the reservoir zones.It is also notable that most of the drilling companies are using LCM as a treatment to this issue.After a survey among the drilling companies, it has been noted that the most used LCM is the calcium carbonate material.Therefore, for the purpose of comparison, different sizes (fine, medium and coarse) of the used CaCO3 LCM have been collected from drilling companies and brought to the laboratory as shown in Fig. 5.

Reference Mud
Water-based mud (WBM) was used as the reference mud (RM) for the experimental studies.It was made using only bentonite and caustic soda (NaOH) as a conventional chemical material.The reference mud was made up of 80 grams of Bentonite, 2 grams of caustic soda, and 1400 cc of water.The composition of the reference mud (RM) is shown in Table 5.

Preparation of RM
The concentration of the RM mentioned in Table 5 was mixed, and the reference mud was prepared according to the API-SPEC-13A-2010 standards.Once the mud is prepared, its density, pH and other rheological properties were measured and recorded.The properties of the RM are summarized in Table 6.

Preparation of Mud with CaCO3
As mentioned earlier, for the purpose between comparison of the developed material and the most commonly used conventional LCM, which is CaCO3, different sizes (fine, medium and coarse) of the collected CaCO3 were added separately to the reference mud in order to find out the effect of the size distribution on fluid lost control.Moreover, for determining the effect of the LCM concentration, various concentrations of each size of CaCO3 were added separately also.The LCM concentration was selected on the base of pounds of the LCM material per barrel of the drilling mud (ppb), the selected LCM concentrations started from 5 ppb to 25 ppb with increment of 5 ppb.At the end, a blend of all CaCO3 sizes was added into the RM and various tests were conducted.

Preparation of Mud with PF
As for the mud with CaCO 3 preparation, different sizes (fine, medium and coarse) of the prepared PF beans were added separately to the reference mud in order to find out the effect of the size distribution on fluid lost control.Moreover, for determining the effect of the PF concentration, various concentrations of each size of the PF were added separately also.The PF concentration was selected on the base of pounds of the PF per barrel of drilling mud (ppb), the selected PF concentrations started from 5 ppb to 25 ppb with increment of 5 ppb.At the end, a blend of all PF sizes was added into the RM and various tests were conducted.

Measuring Rheological Properties
The density, pH, plastic viscosity, yield point, and initial and final gel strengths were measured for the reference mud, RM with various sizes and concentrations of CaCO3 and RM with various sizes and concentration of PF.The used apparatuses are shown in Fig. 6, and the test results are shown in Tables 7 and 8.

Fluid Losses Measurements
Despite that, there are lots of studies and experiments of filtrate rate, in this study, the dynamic high pressure high temperature (HPHT) filter press apparatus has been used instead of the standard API filter press (LPLT).Thereby, the results will be more accurate since similar subsurface conditions have been applied here.The differential pressure of 500 psi has been applied in the tests as well as the temperature has been set on 50 °C.Both used pressure and temperature were gotten from the real conditions of the northern Iraqi reservoir fields.A series of tests have been conducted for the RM, RM with various sizes and concentrations of CaCO3 and RM with different sizes and concentrations of PF.The filtration test results are shown in Tables 9 and 10.

Discussion
The efficiency of different sizes of CaCO 3 as common commercial LCM were evaluated by measuring fluid filtration loss at 500 psi and 50 °C using HPHT filter press.A reduction in the fluid loss was seen after measuring it at 30 minutes.According to Fig. 8, at the concentrations of 5 ppb, 10 ppb, 15 ppb and 20 ppb of fine CaCO3, the mud filtrate volume (30 min) was reduced by 14%, 32%, 44% and 47% respectively, as compared to the reference fluid.While the filtrate volume (30 min) was increased again with increasing the concentrations of the fine sized of CaCO3 to 25 ppb and 30 ppb which reduced the filtrate rate by 44% and 31% respectively.Therefore, it is decided that the upper limit of fine sized CaCO3 to be 20 ppb (which reduces the fluid loss by 47% compared to the RM) and not to excess this limit.For that the addition of 25 ppb and 30 ppb of fine sized CaCO3 has been skipped in other measurements such as rheological measurements.Moreover, the effect of adding medium sized CaCO3 on filtration losses was evaluated.According to Fig. 9, at the concentrations of 5 ppb, 10 ppb and 15 ppb of medium sized CaCO3, the mud filtrate volume (30 min) was reduced by 46%, 44% and 43% respectively, as compared to the reference fluid.As it could be observed from the results, that the optimum concentration of medium sized of CaCO3 to be added was 5 ppb.Above this concentration, the loss reduction will be lower for higher concentration.Furthermore, the effect of adding coarse sized CaCO3 on filtration losses were evaluated as well.According to Fig. 10, at the concentrations of 5 ppb, 10 ppb and 15 ppb of coarse sized CaCO3, the mud filtrate volume (30 min) was reduced by 28%, 27% and 9% respectively, as compared to the reference fluid.As it could be observed from the results, that the optimum concentration of coarse sized of CaCO3 to be added was 5 ppb.Above this concentration, the loss reduction will be lower for higher concentration.Finally, the effect of adding 15 ppb of a blend of all sizes (5 ppb fine, 5 ppb medium and 5 ppb coarse) of CaCO3 was evaluated also.As it can be seen from Fig. 11, with the addition of this blend to the mud, the filtration volume will be reduced by about 44% (from 32 ml to 17.7 ml).
Once the adding CaCO3 tests done, a similar procedure and tests for evaluating the addition of various sizes and concentrations of PF as an environmentally friendly filtration control agent were conducted.The results of various concentrations of fine, medium, coarse and blended sized PF are shown in Figs.12-15.According to Figs. 12-15, the fluid losses reductions by the additions of PF are as following; for fine sized PF; the filtrate volume was reduced by 67%, 73%, 76% and 79% by the addition of 5 ppb, 10 ppb, 15 ppb and 20 ppb of PF respectively.In case of medium sized PF, the reductions were 63%, 73%, 75% and 76% by the addition of 5 ppb, 10 ppb, 15 ppb and 20 ppb of PF respectively.Meanwhile, the fluid losses volume through adding coarse sized PF were reduced by 19%, 41%, 52%, 64% and 72% by the addition of 5 ppb, 10 ppb, 15 ppb, 20 ppb and 25 ppb of PF respectively.Finally, it could be noted that the filtrate volume was reduced by 76% by adding 15 ppb of a blend of sizes (5 ppb fine, 5 ppb medium and 5 ppb coarse) of the PF.
It could be observed from the PF charts, that most fluid loss volume reductions achieved were 79% for 20 ppb of fine sized, 76% for 20 ppb of medium sized, 76% for 15 ppb blended sizes and 76% for 15 ppb of fine sized.Therefore, the competition will be among these four concentrations and sizes.However, by checking table 8, it could be observed that the first three concentrations and sizes (20 ppb fine, 20 ppb medium and 15 ppb of blended sizes) will reduce both pH and density more that the later concentration and size (15 ppb fine).For that, it could be decided that the optimum size and concentration for the PF to be added as a natural LCM are fine and 15 ppb respectively which reduces the fluid loss volume by 76%.Whereas, the optimum size and concentration for the CaCO3 LCM was fine and 20 ppb, respectively, which reduces the fluid loss volume by 47%.
To conclude, it is very clear that the PF acts much better than the most commonly used conventional LCM, CaCO3 in term of filtrate control since the filtrate will be reduced by 76% with only 15 ppb of the fine sized PF while in order to reduce the filtrate by 47%, 20 ppb of the CaCO3 will be required (which means higher solid contains).In addition to that the PF overcomes the CaCO3 in term of availability, cost, naturality and environmente.

Conclusions
• A series of HPHT filtration tests have been conducted on the most common conventional LCM, CaCO3, in order to be the base for comparison the effectiveness of the developed natural LCM.• Moreover, different sizes and concentrations of both CaCO3 and PF were used in order to obtain the effect of LCM particle size distributions and concentrations on fluid loss control.• In addition to the filtration tests, density, pH, viscosity, yield point and gel strength of the mud with and without the additives have been measured.• The filtration test shows that the filtrate rate of the reference mud (without additives) was 32 milliliters in 30 minutes.• The most achieved reduction in the fluid losses with the addition of CaCO3 LCM was about 47% (16.9 ml/30 min.)and this was by the addition of 20 ppb of the fine sized CaCO3 into the reference mud.• Whereases, 76% reduction in fluid losses (7.7 ml/30 min.)was obtained by adding only 15 ppb of the fine sized PF. • This achievement has proven the effectiveness of the developed natural LCM besides that the PF overcomes the CaCO3 in term of availability, cost and environmentally.

API
Musaab et al. (2019) have summarized the formations that the fluid might be loss in four types as shown in Fig. 1, they are; natural fractured formations, caves or vugs, induced fractures and unconsolidated formations.

Fig. 6 .
Fig. 6.Apparatuses used for measuring the rheological properties of the fluids

Fig. 11 .
Fig. 11.Effect of blend of sized CaCO 3 on fluid losses

Table 1 .
Loss severity classification

Table 2 .
Some lost circulation materials used in the petroleum industry

Table 3 .
Environmentally friendly materials used as LCMs.

Table 5 .
Composition of the reference mud (RM)

Table 6 .
Composition of the reference mud (RM)

Table 7 .
Rheological properties of the reference mud with various sizes and concentrations of CaCO3

Table 8 .
Rheological properties of the reference mud with various sizes and concentrations of PF

Table 10 .
fluid losses rate of the reference mud with various sizes and concentrations of PF