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Section 3. Technical sciences in general
https://doi.org/10.29013/AJT-23-5.6-14-19
Kobilov Nodirbek, Khamidov Basit, Shukurov Abror, Kodirov Sarvar, Khidirov Muso, Shukhratov Jahongir,
Institute of General and Inorganic Chemistry of Uzbekistan Academy of Sciences
INVESTIGATION OF PHYSICAL CHEMICAL PROPERTIES OF DRILLING FLUIDS FOR DRILLING OIL AND GAS WELLS
Abstract. The objective of this work is investigation of physical and chemical properties and development new receipt of weighted drilling fluids for drilling oil and gas wells. In the article the main physical and chemical properties of the weighted drilling fluids for drilling oil and gas wells have been given. The methods of testing drilling fluids and materials used for obtaining weighted drilling fluids have been investigated.
Keywords: drilling fluid, properties, test, standards, weighting, receipt, well, oil and gas.
Introduction (CST), return permeability, X-ray diffraction and
The properties of drilling fluids play important role particle-size distribution (PSD). for oil and gas well drilling. Drilling fluid density is usu- Materials and methods
ally called mud weight. Normal pressure formations As a material for obtaining drilling fluids used generally have a pressure gradient similar to a water gra- water, bentonite, carboxymethyl cellulose, gossypol dient. For various reasons formation fluid pressures are resin, barite (BaSO4) and NaOH, Na2CO3. Investiga-frequently higher. Barite or hematite is used to increase tions of drilling fluids properties carried out according the drilling fluid density. This increases the hydrostatic API (API RP 13-B1, B2) standards. The viscosity is degradient in the well bore so that the pressure in the well fined as the resistance offluid to flow. The concepts of bore is higher than formation pressure [1; 2]. viscosity, shear stress, and shear rate are important in
The most essential properties of drilling fluids are understanding the flow characteristics of fluids. Spe-
viscosity, mud weight or density, filter cake, Solid's cific measurements are made on fluids to determine
content, gel strength toxicity, fluid rheology, fluid rheological parameters under a variety of conditions.
loss, particle plugging, high-angle sag and dynamic Determination of viscosity using the Marsh funnel. high-angle sag, high-temperature fluid aging, cut- Determination of viscosity and/or gel strength
tings erosion, shale stability, capillary suction time using a direct-indicating viscometer.
The viscosity of drilling fluid is a function of:
- Viscosity of the continuous phase or the base liquid;
- The size, shape and solids particles in the mud which is represent it by the plastic viscosity;
- The inter-particle force represents it by the yield point.
The plastic viscosity is the resistance to flow caused by the friction between solid particles. The yield point is the resistance to the initial flow or the stress required to start flowing. The yield point is measured under flowing conditions.
Reducing viscosity in any drilling fluid can be achieved by:
- Reduction of solids by mechanical treatment or dilution;
- Neutralization of attractive forces between particles [3; 4].
Mud weight or density
The density is the weight per unit of volume. During operations mud weight has to be well controlled and need adjustment. If the mud weight is less than the required level of density to drilling safely can permit the formation fluids to flow into the well and lead to well control situation and if it is higher than the appropriate level it can lead to lost circulation situations. Mud weight were tested by 4-scale Metal Mud balance. The real mud weight under circulation is greater than the density while drilling fluid is in static. This density is called equivalent circulating density (ECD). When designing hydraulics, the ECD has to be less than fracture gradient [5].
Filter cake
The filter cake is formed when mud solids deposit on the walls of the hole. The filtration is the loss of fluids from mud into the formation. The main objective of controlling fluid loss is forming thin filter cakes while drilling through permeable formations and preventing excessive fluid loss (filtrate).
Loss of drilling fluids in formation can lead to high water consumption and thick filter cake which
can cause a tight hole, increased torque and consequently lead to stuck pipe.
Solids content
Solids can be:
- Added to the drilling fluid in order to increase viscosity or weight;
- Accumulated in the fluid like drilled cuttings or disintegrated clay particles.
The treatment of solids has to be effective to remove undesired solids which do not contribute to beneficial properties.
Gel strength
Gel strength represents the attractive forces under static conditions (non-flow conditions). Contrary to gel strength, the yield point represents the attractive forces under flowing conditions. The gel strength gives an indication of the required pressure to initiate flow after ceasing circulation for period of time. Also, it gives an indication about the ability of the drilling fluid to suspend cuttings when mud is stationary.
Gels are classified into two types:
- Progressive that starts low but increase with time;
- Fragile that starts high and increase slightly with time.
Toxicity
The environmental and toxicity standards of the region in which the fluid is being used will require testing either of the whole drilling fluid or of its individual components. Toxicity tests generally are used for offshore applications. An approved laboratory can perform the proper testing to ensure compliance of the fluid or its components.
Fluid rheology
Fluid rheology is an important parameter of drilling-fluid performance. For critical offshore applications with extreme temperature and pressure requirements, the viscosity profile of the fluid often is measured with a controlled-temperature and -pressure viscometer (e.g., the Fann iX77 Rhe-ometer). Fluids can be tested at temperatures of < 35 °F to 500 °F, with pressures of up to 20.000 psia.
Cold-fluid rheology is important because of the low temperatures that the fluid is exposed to in deepwa-ter risers. High temperatures can be encountered in deep wells or in geothermally heated wells. The fluid can be under tremendous pressure downhole, and its viscosity profile can change accordingly.
Fluid loss
If fluid (or filtration) loss is excessive, the following can occur:
- Formation instability;
- Formation damage;
- Fractured formation and loss of drilling fluid.
In the field, LP/LT(Low Pressure/Low Temperature) and HP/HT(High Pressure/High Temperature) fluid-loss tests are performed routinely. Fluid loss also can be measured under dynamic conditions using the Fann Model 90 Dynamic Filtration System, which incorporates a rotating bob to provide fluid shear in the center of a ceramic-filter core. The fluid is heated and pressurized. Fluid loss is measured radially through the entire core, giving a sophisticated simulation of the drilling fluid circulating in the wellbore.
Particle plugging
The particle-plugging test (PPT) often is used to evaluate the ability of plugging particles added to a fluid to mitigate formation damage by stopping or slowing filtrate invasion into a core. A PPT uses an inverted HP/HT-filter-press cell that has been fitted with a ceramic disk as a filtering medium and is pressurized with a hydraulic cylinder. Ceramic disks with different mean pore-throat diameters are used to simulate a wellbore wall. A PPT typically is run with a 2.000-psi or higher differential pressure. The spurt loss and total fluid loss are measured over a 30-minute period. The cell is inverted, and fluid loss is measured from the top of the cell to eliminate the effects of fluid settling.
High-temperature fluid aging
Over time, high temperatures can degrade the components of a drilling fluid, and alter its performance. High-temperature aging of the fluid is conducted to assess the impact that temperatures >
250 °F have on performance. Fluid can be aged statically and dynamically. In the static-aging process, the fluid is placed in a pressurized cell, and allowed to stand without rolling at the desired test temperature for a desired length of time (rarely < 16 hours). This simulates the stress the fluid might be subjected to during static periods in the wellbore (e.g., logging and tripping). In dynamic aging, the fluid is rolled in a pressurized cell at the desired test temperature to simulate the fluid under drilling conditions. After undergoing aging, the fluid can be evaluated using the same tests that are applied to non-aged fluid.
Shale stability
Reactive shales cause many difficulties in a drilling operation. Fluids should be designed to mitigate these shale problems. Along with erosion testing, four other distinct tests are used to assess the interaction between the drilling fluid and shale: capillary suction time (CST), return permeability, X-ray diffraction and particle-size distribution (PSD). CST
The CST test investigates the chemical effects of the drilling fluid on the dispersive properties of shale and active clays. The CST test measures filter-cake permeability by timing the capillary action of filtrate onto a paper medium. Changes in permeability then can be related to the inhibitive characteristics of the fluid [4].
Return permeability
When drilling reaches a hydrocarbon-bearing zone, of great concern is the potential to damage the formation and thereby to reduce the ability of the well to produce hydrocarbons. A return-permeability test can reveal formation damage, and can be conducted using a return permeameter.
X-ray diffraction
Knowing the mineral composition of a formation to be drilled is important for determining how the drilling fluid will react with the formation, and how to prevent potential drilling problems. Fluid labs use X-ray diffraction to determine the mineralogi-cal composition of shale or cuttings. They expose a
crystalline mineral sample to X-ray radiation, and compare the resultant diffraction pattern to known standards to determine which minerals are present in the sample.
Result and discussions
Not only our investigations but also the American Petroleum Institute (API) publishes documents relating to oilfield standards, including drilling fluids testing procedures. As with any laboratory procedure
requiring the use ofpotentially hazardous chemicals and equipment, the user is expected to have received proper training and knowledge in the use and disposal of these potentially hazardous materials. The user is responsible for compliance with all applicable local, regional, and national requirements for worker and local health, safety, and environmental liability.
Ivestigations of physical chemical properties of drilling fluids are given on Figire 1.
Concentration of reagent MBR,% Figure 1. Dependence of water filtration (1), pH(2), Viscosity (3) and stabilization index (4) from concentration of CCR
The results of mnvestigations show that on basis of the chemical reagent MBR, CMC and barite we can receive weighted drilling fluid with a density of 1.55-2.40 g/cm3. The pH of the heavy mud on basis of the composite chemical reagent reaches 9-10 or without the addition of caustic soda. Concentration barite is 40-60%. The composite chemical reagent also has a
Table 1.- Typical
positive effect on the flow properties as well as filtering solution decreased from 12 to 5 cm3/30 min. Stabilization drilling fluid is one of the main physic-chemical property of drilling mud. Stability drilling fluid is ability of solution to hold particle weighted distribution. It determinates quantity difference of density bottom and top half of the drilling fluid sediment in 24 hours.
Field Tests For WBF
Drilling-fluid density Mud weight, in ppg or equivalent unit of measure, as appropriate to the region [e.g., specific gravity (SG)].
Viscosity Viscosity exhibited when a specific quantity of fluid is poured through a Marsh funnel (typically recorded in seconds per quart).
Rheology Rheological properties exhibited at various rotational speeds using a viscometer (also called rheometer). The Fann* 35 viscometer can test the fluid at multiple speeds and temperatures to give a detailed viscosity profile for the fluid.
Gel strength Suspension characteristics developed over specified time intervals.
* Fann is the registered name for fluids-testing equipment provided by Fann Instrument Co., Houston
Filtration Surface indication of filtrate invasion into the near wellbore (also called fluid loss). Performed under LP/LT conditions and HP/HT conditions as required.
Retort analysis Percentages of water, oil, and solids making up the active system.
Sand content Percentage of sand in the active system.
Methylene blue capacity Clay content in the active system [also commonly called methylene blue test (mbt)].
pH Indication of system acidity or alkalinity.
Chemical analysis: Alkalinity/lime content Chlorides Total hardness (calcium) Indication of variations from base-fluid formulation caused by surface treatment and/or influx or contamination from downhole formations.
Extensive testing of the fluid is performed in the design phase of the fluid, either to achieve desired fluid characteristics or to determine the performance limitations of the fluid.
Laboratory testing aids in fluid design and expands the capacity to monitor and evaluate fluids when field-testing procedures prove inadequate. Some laboratory tests are identical to field-testing methods, whereas others are unique to the laboratory environment. In the laboratory setting, testing and equipment should determine following properties for drilling oil and gas wells:
- Toxicity;
- Fluid rheology;
- Fluid loss;
- Particle plugging;
- High-angle sag;
- Dynamic high-angle sag;
- High-temperature fluid aging;
- Cuttings erosion;
- Shale stability;
- Capillary suction;
- Lubricity;
- Return permeability;
- X-ray diffraction;
- Particle-size distribution (PSD).
Investigations show the successful oil well drilling depends largely on a good mud Program. During drilling, mud provides sufficient hydrostatic pressure, removes drill cuttings and cools drill bits. Mud additives are always required to provide sufficient hydrostatic pressure to ensure borehole stability. Barium Sulphate (BaSO4) also known as barite is the prevalent weighting material but there is need to develop local materials to augment the use of Barite. This study was aimed at assessing the suitability of galena, a lead sulfide (PbS), as an alternative weighting material in drilling fluids.
Conclusions
Based on the above results, we can conclude that the density, stability, viscosity and filtration ofdrilling fluids play main role to drill oil and gas wells without accident. Investigations show that safety drilling oil and gas wells depend on geological conditions and the optimum apparent viscosity value is approximately 40-60 s, for filtration value is 3-8 sm3/30 min, for density value according to the layer pressure and for pH value is 9-10 for water based drilling fluids.
References:
1. API RP 13-Br Recommend Practice for Field Testing Water-Based Drilling Fluids, third edition. 2003. Washington, DC: API.
2. API RP 13-B2. Recommended Practice Standard Procedure for Field Testing Oil-Based Drilling Fluids, third edition. 1998. Washington, DC: API.
3. Patel A. et al. Designing for the Future-A Review of the Design, Development and Testing of a Novel, Inhibitive Water-Based Mud. 2002. Paper presented at the AADE Annual Technology Conference Drilling and Completion Fluids and Waste Management, Houston, 2-3 April. AADE-02-DFWM-HO-33.
4. Kobilov N. S., Negmatova K. S., Sharifov G. N., Rakhimov X. Y. Composite chemical reagent for stabilization heavy mud for drilling salt-anhydrite layer of oil and gas wells // European applied science. II. Germany, 2016.- P. 50-52.
5. Negmatova K. S., Negmatov S. S., Salimsakov Yu. A., Rakhimov H. Y., Negmatov J. N., Isakov S. S., Kobilov N. S. Structure And Properties of Viscous Gossypol Resin Powder. AIP Conference Proceedings 1459, USA, - 300. 2012.- P. 300-302.
6. Https://Doi.0rg/10.1063/1.4738476.
7. Komila Negmatova, Shodilbek Isakov, Nodir Kobilov, 2012. Effective Composite Chemical Reagents Based on Organic And Inorganic Ingredients For Drilling Fluids Used In The Process Of Drilling Oil Wells // Advanced Materials Research. Trans Tech Publication, Switzerland.- Vol. 413.- P. 544-547.
8. Kobilov N. S., Dusmurodov E. B., Kodirov S. A., Khidirov M. Q Khujamov A. Research and development of effective composite chemical reagents for drilling fluids. An International Multidisciplinary Research Journal. ISSN: 2249-7137.- Vol. 10.- Issue 10. 2020. URL: https://saarj.com
9. Kobilov N. S., Kamolova Z., Shukurov A., Xushnazarov Sh., Sulaymonov I., Khalimov A., Abdura-khmonova N. Development of New Composite Chemical Reagents and Their Implementation/ International Journal of Advanced Research in Science, Engineering and Technology, - Vol. 8.-Issue 1.- January 2021.- P. 16453-16457. URL: https://ijarset.com
10. Kobilov N. S., Negmatov S. S., Yu. Salimsakov A., Sobirov B. B., Negmatova K. S., Rakhmanov B. Sh. Research and Development of Manufacture Technology of Polymeric Composite Materials of Electro-technical Purpose Filled with Hydrolytic Lignin. 2008. AIP Conference Proceedings.- Vol. 1042.-Issue 10.1063/1.2989016/ URL: https://doi.org/10.1063/L2989016
