Description:Field of the Invention

[0001] The present invention generally relates to loss circulation materials. In particular, the present invention relates to a loss circulation material composition that is reservoir-friendly, acid-soluble, and exhibits high-pressure stability for use during well operations.

Background of the Invention

[0002] Loss circulation, which refers to undesirable migration of drilling fluids from the wellbore into surrounding geological formations, presents significant operational and economic challenges in the oil and gas industry. The severity of fluid loss is largely determined by the characteristics of the formation with naturally fractured, vugular, or highly permeable zones. When drilling fluids are lost to these susceptible formations, there is not only a direct increase in operational costs, but also a compromise in wellbore stability that results in elevated operational risk.

[0003] To address these problems, loss circulation materials (LCM) serve as a vital remedial measure during drilling operations. LCMs are introduced along with drilling fluids to bridge, plug, or seal the loss zones, thereby restoring circulation and maintaining well integrity. However, selection and performance of LCMs are influenced by factors such as the size and geometry of the formation voids, compatibility with drilling fluids, ease of placement, and the ability to withstand downhole pressures and temperatures. Despite the widespread use of LCMs, achieving an optimal balance between effective sealing and minimal formation damage remains a persistent challenge.

[0004] Moreover, conventional LCMs often exhibit limited efficacy in formations with diverse pore structures and fracture apertures, frequently necessitating repeated applications. Such limitations can result in suboptimal bridging, incomplete sealing of loss zones, and the accumulation of residual solids, which may negatively impact reservoir productivity by reducing permeability and impeding hydrocarbon flow. Additionally, many conventional LCMs are characterized by poor degradability, potential toxicity, which poses significant regulatory and ecological concerns, particularly, in sensitive or offshore drilling environments.

[0005] Further, conventional LCMs are insoluble in acid, which reduces the porosity and permeability of production zones in the formations. Also known LCMs are often incompatible with other additives in the drilling fluids. Under such circumstances, LCMs are often found ineffective and needs multiple applications, which affects the reservoir conditions.

[0006] Therefore, in light of the above-mentioned drawbacks, there is a need for improved LCM that is capable of effectively sealing a broad spectrum of loss zones with varying pore and fracture sizes. There is a need for improved LCM that is compatible with diverse drilling fluids and minimizes long-term damage to reservoir. There is a need for an improved composition that demonstrates high-pressure stability and effectively reduces fluid loss during drilling operations.

Summary of Invention

[0007] In various embodiments of the present invention a loss circulation material composition is provided. The composition comprises polyvinyl alcohol polymer, viscosifier, strengthening agent, fluid loss control additive, and calcium carbonate. In an embodiment of the present invention, the LCM composition comprises polyvinyl alcohol polymer in an amount of 7% W/V, viscosifier in an amount of 1.4% W/V, strengthening agent in an amount of 45% W/V, fluid loss control additive in an amount of 1% W/V, and calcium carbonate in an amount of 45% W/V. The loss circulation material of the present invention is effective in sealing a broad spectrum of loss zones with varying pore and fracture sizes.

[0008] In an embodiment of the present invention, the viscosifier of the composition is xanthan gum. The strengthening agent of the composition is sodium chloride. The fluid loss control additive of the composition is polyanionic cellulose. The calcium carbonate is a combination of four different grades of calcium carbonates comprising PSD-CAL CARB (80–150 microns), PSD-CAL CARB (1200–3300 microns), PSD-CAL CARB (3000–5000 microns), and PSD-CAL CARB (4000–8000 microns). The four different grades of calcium carbonates are in the ratio of 10:10:10:15 respectively. In an embodiment of the present invention, the density of the LCM composition is in a range from 1.4 to 1.5 g/cm3.

[0009] In an embodiment of the present invention, a process for preparing a loss circulation material composition for use in drilling operations is provided. The process comprises mixing water with polyvinyl alcohol to form an aqueous polyvinyl alcohol solution. Subsequently, a pre-determined amount of viscosifier is added to the polyvinyl alcohol solution to obtain a first solution. To the first solution, a pre-determined amount of strengthening agent is added to obtain a second solution. Further, to the second solution, a predetermined amount of fluid loss control additive is added to obtain a third solution. The process further comprises adding a predetermined amount of calcium carbonate to the third solution to obtain the loss circulation material composition.

Brief Description of the Drawings

[0010] The present invention is described by way of embodiments illustrated in the accompanying drawings wherein:

[0011] FIG. 1 is a flow chart illustrating a process for preparation of a loss circulation material composition, in accordance with an embodiment of the present invention.

Detailed Description of the Invention

[0012] In an embodiment of the present invention, a loss circulation material composition (LCM) is provided. The LCM of the present invention is effective in sealing broad spectrum of loss zones with varying pore and fracture sizes. Further, the LCM composition of the present invention effectively reduces fluid loss during drilling operations with high pressure stability and also exhibits compatibility across diverse drilling fluids, in accordance with various embodiments of the present invention.

[0013] The disclosure is provided in order to enable a person having ordinary skill in the art to practice the invention. Exemplary embodiments herein are provided only for illustrative purposes and various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. The terminology and phraseology used herein is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed herein. For purposes of clarity, details relating to technical material that is known in the technical fields related to the invention have been briefly described or omitted so as not to unnecessarily obscure the present invention.

[0014] In an embodiment of the present invention, the LCM composition comprises, water, polyvinyl alcohol polymer, viscosifier, strengthening agent, fluid loss control additive, and calcium carbonate. In an exemplary embodiment of the present invention, the LCM composition comprises polyvinyl alcohol polymer in an amount of 7% Weight by Volume of Water(W/V), viscosifier in an amount of 1.4% (W/V), strengthening agent in an amount of 45% (W/V), fluid loss control additive in an amount of 1% (W/V), and calcium carbonate in an amount of 45% (W/V).

[0015] In an embodiment of the present invention, the polyvinyl alcohol polymer functions as both a binder and a film-forming agent within the LCM composition, contributing to structural integrity and cohesion of the LCM composition. The polyvinyl alcohol aids in holding together the constituents of LCM composition. Further, polyvinyl alcohol also creates a cohesive matrix that enhances the structural integrity of the material. This is essential to LCMs as maintaining the integrity of the plug or seal is critical for preventing fluid migration and loss. Polyvinyl alcohol is a water-soluble, biodegradable, and colourless polymer, which is critical for generating reinforcing fibres within the LCM composition, thereby enhancing structural integrity and performance of the LCM composition. The structure of polyvinyl alcohol allows it to generate reinforcing fibres within the LCM composition. These fibres interlock and create a network that significantly improves the mechanical strength and cohesion of the material, making it more resistant to breakdown under downhole conditions.

[0016] In an embodiment of the present invention, the viscosifier increases viscosity and gel strength of the LCM composition, thereby enhancing its suspension capabilities and transport efficiency. In an exemplary embodiment of the present invention, xanthan gum is used as the viscosifier due to its biopolymeric nature, thereby exhibiting high shear-thinning and pseudoplastic properties which are advantageous for drilling fluid applications. Owing to the high shear-thinning characteristic, viscosity decreases under high shear rates (such as during pumping) but increases at low shear rates (such as when the fluid is static). This dynamic rheological behaviour ensures optimal performance of the drilling fluid. In another embodiment of the present invention, Xanthan gum in the LCM composition facilitates easy pumping and placement of the drilling fluid while maintaining strong suspension and carrying capacity when circulation slows or stops.

[0017] In an embodiment of the present invention, the strengthening agent is incorporated to improve mechanical properties and resistance of the LCM composition against deformation and erosion under downhole conditions. In an exemplary embodiment of the present invention, sodium chloride (NaCl) is used as the strengthening agent which helps in reinforcing the LCM composition and also for regulating osmotic pressure and salinity levels. Under operational conditions where formation fluid is more saline than drilling fluids, the formation water moves from the drilling fluid into the formation by osmosis, causing clay minerals to hydrate and swell. This swelling leads to wellbore instability, tight holes, stuck pipe, and even wellbore collapse. By increasing the salinity of the drilling fluid with NaCl as the strengthening agent in the LCM composition, the osmotic gradient is reduced or reversed, minimizing water movement into the formation. This helps keep the clay particles stable, preventing swelling and dispersion, and thus maintaining wellbore integrity.

[0018] In this embodiment of the present invention, the composition comprises fluid loss control additive to minimize volume of drilling fluid that escapes from the LCM composition into surrounding geological formation. In an exemplary embodiment of the present invention, poly anionic cellulose is utilized as the fluid loss control additive, due to its cellulose-based structure that imparts superior water retention and filtration control characteristics of the LCM. Advantageously cellulose fluid loss additives such as polyanionic cellulose, forms a thin, low-permeability filter cake on the wellbore wall. This filter cake acts as a barrier, further reducing the invasion of drilling fluid into the formation. Advantageously, by limiting the amount of fluid that leaks into the formation, the polyvinyl alcohol enhances the sealing efficiency and ensures long-term stability of LCM plug formed within fractures or voids encountered during drilling operations.

[0019] Surprisingly minimal amount of polyvinyl alcohol in the LCM composition achieves improvement in rheological stability of drilling fluid and improve fluid loss control. The molecular structure of polyanionic cellulose enables it to bridge and bind particles effectively, leading to the quick formation of a low-permeability filter cake even at low dosages.

[0020] In this embodiment of the present invention, the calcium carbonate is utilised as a particulate material to impart effective bridging and plugging capabilities to the LCM composition. The calcium carbonate is incorporated in multiple grades and particle size distributions to create a multi-modal particulate system, thereby enabling sealing of a wide range of fracture and pore sizes within geological formation and acts as a barrier preventing the undesirable invasion of drilling fluids into the formation. In an exemplary embodiment of the present invention, the LCM composition comprises four distinct grades of calcium carbonate: PSD-CAL CARB (80–150 microns), PSD-CAL CARB (1200–3300 microns), PSD-CAL CARB (3000–5000 microns), and PSD-CAL CARB (4000–8000 microns), which are blended in a ratio of 10:10:10:15, respectively.

[0021] The smaller particles of calcium carbonate fill the finer pores, while the larger particles bridge and seal wider fractures, resulting in a more effective and comprehensive plugging/sealing mechanism. This property ensures well cleanup and enhances the overall oil and gas production. Calcium carbonate, due to its particle size and high surface area, allows them to effectively fill micro-pores and bridge fine fractures that larger particles cannot. This results in a more comprehensive sealing of the formation, reducing the risk of lost circulation and associated non-productive time. Further, calcium carbonate is acid soluble, which advantageously allows easy removal after drilling operations by acidizing the wellbore, which is critical in hydrocarbon pay zones.

[0022] In an exemplary embodiment of the present invention, the subsurface formations have a gross permeability range of 50 to 5000 microns including fractures. The maximum pore/fracture size observed within these formations is 5000 microns corresponding to the upper limit of the measured permeability range. Fluid loss ranging from minor to severe has been encountered within these permeable zones with the severity of loss directly related to the permeability and pore/fracture size present in the formation. The effectiveness of loss circulation remedies depends on the size, geometry, and concentration of bridging agents in the mud. Calcium carbonate with particle sizes from 80 to 5000 microns has been used in the LCM composition to ensure effective bridging.

[0023] In an embodiment of the present invention, the LCM composition along with drilling fluid is pumped into the wellbore and positioned across the fracture zone. Advantageously, the LCM composition has demonstrated a surprising effect in sealing slit with aperture sizes ranging from 1000 to 5000 microns simulating fractured and vuggy limestone and steel balls representing highly permeable formations. Surprisingly, plugs formed by the LCM withstands pressures up to 1000 psi without compromising on its mechanical properties and performance. Additionally, the LCM composition serves as an effective sealant and exhibits acid solubility, making it compatible with reservoir conditions and allowing easy removal and cleanup after the drilling operation is completed. Furthermore, advantageously, the LCM composition is readily degradable in 15 percent hydrochloric acid, thereby ensuring complete dissolution without causing any reservoir blockage or impairment. This improved property of the LCM facilitates efficient post-treatment cleanup and preserves reservoir integrity. Table 1 below provides comparative data table illustrating the degradability of the LCM composition of the present invention over convention LCM compositions.

Table 1
Sl No Details of LCM Acid degradability in 15% Hydrochloric Acid
1 Fiber based LCM (Conventional) Poor degradability
2 Clay based LCM (Conventional) Poor degradability
3 Mica based LCM (Conventional) Poor degradability
4 Present Invention Fast rate of degradation (soluble in 6 hours leaving no residue)

[0024] Table 1 above indicates that the LCM composition according to the present invention is wholly acid degradable in 15% hydrochloric acid (HCl) while the conventional LCMs based on fibre, clay and mica are poorly degradable. Further, in an exemplary embodiment of the present invention, the LCM composition is dissolved in the acid completely within 6 hours leaving no residue. In an embodiment of the invention, the density of the LCM composition is in a range from 1.4 to 1.5 g/cm3.

[0025] In an embodiment of the present invention, a process for preparing the LCM composition is provided. FIG. 1 is a flow chart illustrating a process for preparation of a LCM composition, in accordance with an embodiment of the present invention.

[0026] At step 102, a predetermined amount of water is mixed with a predetermined amount of polyvinyl alcohol to obtain a polyvinyl alcohol solution. In an embodiment of the present invention, the predetermined amount of polyvinyl alcohol is 7% (W/V) to ensure optimal performance. In an embodiment of the present invention, polyvinyl alcohol is gradually added to the water and agitated continuously for a predetermined duration, preferably 30 to 40 minutes, resulting in formation of homogeneous aqueous solution of polyvinyl alcohol. The polyvinyl alcohol solution serves as an effective carrier medium for other components of the LCM composition.

[0027] At step 104, a predetermined amount of viscosifier is added into the polyvinyl alcohol solution to obtain a first solution. In an embodiment of the present invention, the viscosifier is xanthan gum which is a high molecular weight polysaccharide that imparts viscosity at low concentrations. In an exemplary embodiment of the present invention, the predetermined amount of xanthan gum is 1.4% (W/V). In an embodiment of the present invention, xanthan gum is gradually added to the polyvinyl alcohol solution over a predetermined duration, preferably 10 to 15 minutes under high shear mixing conditions. The high shear mixing prevents formation of undissolved agglomerates and ensures uniform distribution of the viscosifier throughout the solution. The addition of viscosifier increases the viscosity and improves homogeneity and optimal performance of the LCM composition.

[0028] At step 106, a predetermined amount of strengthening agent is added to the first solution to obtain a second solution. In an embodiment of the present invention, the strengthening agent is sodium chloride (NaCl) that enhances tensile strength and durability of the fibres in the LCM composition. In an exemplary embodiment of the present invention, the predetermined amount of sodium chloride is 45% (W/V). In an embodiment, sodium chloride is added gradually and subjected to high-speed mixing for a predetermined duration, preferably 10 minutes to ensure complete dissolution of the sodium chloride. This step is essential for reinforcing mechanical integrity of the fibres, thereby improving overall robustness and performance of the LCM composition under challenging downhole conditions.

[0029] At step 108, a predetermined amount of fluid loss additive is added to the second solution to obtain a third solution. In an embodiment of the present invention, the additive is PAC, that helps in reducing fluid loss and further enhances viscosity of the LCM composition. In an exemplary embodiment of the present invention, the predetermined amount of PAC is 1% (W/V). In an embodiment of the invention, the fluid loss additive is added gradually added and subjected to high-speed mixing for a predetermined duration, preferably 15 minutes to ensure thorough dispersion of PAC. The third fluid loss additive significantly improves its effectiveness in preventing seepage through porous formations and thereby contributing to overall performance and stability of the LCM composition.

[0030] At step 110, a predetermined amount of calcium carbonate is added to the third solution to obtain the LCM composition. In an embodiment of the present invention, the predetermined amount of calcium carbonate is 45% (W/V) In an embodiment of the present invention, four different grades of calcium carbonates, having different particle size are added. In an exemplary embodiment of the present invention, the four different calcium carbonate grades include (1) PSD (80–150 microns), (2) PSD (1200–3300 microns), (3) PSD (3000–5000 microns), and (4) PSD (4000–8000 microns), which are in a ratio of 10:10:10:15, respectively. In an embodiment of the present invention, various grades of calcium carbonate are employed to maximize bridging and sealing efficiency across various formation pore and fracture sizes. In an embodiment of the present invention, each grade of calcium carbonate is added sequentially by mixing at a low speed for 5 minutes per grade to ensure uniform dispersion and optimal integration of all particulate components. In an embodiment of the present invention, the adding and mixing of the different grades of calcium carbonate is performed using an industrial grade mixing apparatus to achieve thorough homogenization. In an embodiment of the present invention, the process for preparation of the LCM composition is carried out at a temperature of 24 + 2 degrees Celsius.

Working Examples

Preparation of LCM Composition

[0031] 500ml of water was gradually added to 35 gm polyvinyl alcohol and mixed for 40 minutes. Subsequently, 7.0 gm of xanthan gum was gradually added to the polyvinyl alcohol solution and mixed for a duration of 15 minutes under high shear mixing conditions. Subsequently, 225 gm of sodium chloride was gradually added and mixed for 10 minutes. Further, 5.0 gm of polyanionic cellulose was gradually added and subjected to a high-speed mixing for 15 minutes. Further, 50 gm of PSD (80–150 microns), 50 gm of PSD (1200–3300 microns), 50 gm of PSD (3000–5000 microns), and 75gm of PSD (4000–8000 microns) were added sequentially subjected to mixing for 5 minutes per grade of calcium carbonate to obtain the LCM composition. The process of preparing LCM composition was carried out at a temperature of 24 + 2 degrees Celsius.

[0032] The performance of the LCM obtained from above process was evaluated against varying slit sizes representing different loss conditions and the data is provided in Table 2 below.

Table 2
Loss type Aperture size of slit (µ) Particle Composition Concentra-tion (ppb) Max. Pressure hold (psi) Performance time
Volume of drilling fluid loss (ml)
seepage to partial 1000 10:10:10:15 45 1000 30 <100
partial to moderate 3000 10:10:10:15 45 1000 30 <100
moderate to severe 5000 10:10:10:15 45 1000 30 <100

[0033] As shown in table 2, the LCM consistently withstood 1000 psi pressure for 30 minutes while exhibiting minimal drilling fluid loss. This confirms that the LCM successfully sealed aperture size up to 5000 microns a moderate-severe loss condition at a much lesser concentration of 45 ppb even at higher pressure conditions (1000psi) underscoring its superior performance.

[0034] Moreover, the LCM material in the present invention is compatible with various types of drilling fluid systems such as water-based drilling fluid systems like KCl-PHPA-polyol drilling fluid, low-toxicity synthetic oil-based drilling fluid, and non-damaging drilling fluid systems. The LCM of the present invention is also compatible with micro-bubble-based mud systems, demonstrating its broad applicability.

[0035] In accordance with various embodiments of the present invention, advantageously, the LCM composition provides improved performance in drilling operations. Also, the composition is formulated to generate fibres that efficiently bridge and seal a wide range of pore and fracture sizes, resulting in highly effective fluid loss control. This minimizes formation damage and reduces environmental impact. Furthermore, the LCM composition is both biodegradable and acid-soluble, ensuring that it acts as a temporary yet robust barrier in loss-prone formations. After acidization, the LCM leaves no residual damage, thereby enhancing reservoir productivity and improving operational efficiency.

[0036] While the exemplary embodiments of the present invention are described and illustrated herein, it will be appreciated that they are merely illustrative. It will be understood by those skilled in the art that various modifications in form and detail may be made therein without departing from the scope of the invention.
, Claims:We Claim:

1. A loss circulation material composition comprising:
a polyvinyl alcohol polymer in an amount of 7 % W/V;
a viscosifier in an amount 1.4 % W/V;
a strengthening agent in an amount of 45% W/V;
a fluid loss control additive in an amount of 1% W/V; and
calcium carbonate in an amount of 45% W/V,
wherein the loss circulation material composition is acid-degradable and capable of withstanding pressures up to 1000 psi and capable of sealing pores/fractures up to 5000 microns.

2. The composition as claimed in claim 1, wherein the viscosifier is xanthan gum.

3. The composition as claimed in claim 1, wherein the strengthening agent is sodium chloride.

4. The composition as claimed in claim 1, wherein the fluid loss control additive is polyanionic cellulose.

5. The composition as claimed in claim 1, wherein the calcium carbonate is a combination of four different grades of calcium carbonates comprising PSD-CAL CARB (80–150 microns), PSD-CAL CARB (1200–3300 microns), PSD-CAL CARB (3000–5000 microns), and PSD-CAL CARB (4000–8000 microns)

6. The composition as claimed in claim 5, wherein the four different grades of calcium carbonates comprising PSD-CAL CARB (80–150 microns), PSD-CAL CARB (1200–3300 microns), PSD-CAL CARB (3000–5000 microns), and PSD-CAL CARB (4000–8000 microns) are in a ratio of 10:10:10:15 respectively.
7. The composition as claimed in claim 1, wherein the density of the LCM composition is in a range from 1.4 to 1.5 g/cm3.

8. A process for preparing a loss circulation material composition for use in drilling operations, the process comprising:

Step a) mixing water with polyvinyl alcohol to form an aqueous polyvinyl alcohol solution;
Step b) adding a predetermined amount of viscosifier to the polyvinyl alcohol solution to obtain a first solution;
Step c) adding a predetermined amount of strengthening agent to the first solution to obtain a second solution;
Step d) adding a predetermined amount of fluid loss control additive to the second solution to obtain a third solution; and
Step e) adding a predetermined amount of calcium carbonate to the third solution to obtain the loss circulation material composition.

9. The process as claimed in claim 8, wherein the predetermined amount of polyvinyl alcohol is 7% (W/V).

10. The process as claimed in claim 8, wherein the predetermined amount of viscosifier 1.4% (W/V).

11. The process as claimed in claim 8, wherein the predetermined amount of strengthening agent is 45% (W/V).

12. The process as claimed in claim 8, wherein the predetermined amount of fluid loss control additive is 1% (W/V).
13. The process as claimed in claim 8, wherein the predetermined amount of calcium carbonate is 45% (W/V).

14. The process as claimed in claim 8, wherein the process is carried out under stirring conditions for a predetermined duration in a range of 10-15 minutes for each step.

15. The process as claimed in claim 8, wherein the process for preparation of the LCM composition is carried out at a temperature of 24 + 2 degrees Celsius.

Dated this 15th day of July, 2025

Oil and Natural Gas Corporation Limited

(Jogeshwar Mishra)
IN/PA - 2578
of Shardul Amarchand Mangaldas & Co.
Attorneys for the Applicant