FORMATE-BASED FLUIDS: FORMULATION AND APPLICATION/ISPLAKE NA BAZI FORMIJATA: SASTAV I PRIMJENA

Abstract

Formate-based fluids has been successfully used in over hunders HPHT well operations since they introduced in field practice. They have many advantages when compared with conventional HPHT drilling and completion fluids such as: minimal formation damage, maintenance of additve properties at high temperatures, reduced hydraulic flow resistance, low potential for differential sticking, naturally lubricating, very low corrosion rates, biodegradable and pose little risk to the environment etc. Formate-based fluids can be applied during deep slim hole drilling, shale drilling, reservoir drilling, salt and gas hydrate formations drilling. The laboratory research was carried out to evaluate the rheological behavior of formate-based fluids as a function of temperature. Formate-based fluids were formulated using potassium formate brine, xanthan polymer, PAC, starch and calcium carbonate. Experimental results show that potassium formate improves the thermal stability of polymers. [PUBLICATION ABSTRACT]

Headnote

Key words: formate-based fluids, potassium formate, high temperature, fluid properties, drilling

Abstract

Formate-based fluids has been successfully used in over hunders HPHT well operations since they introduced in field practice. They have many advantages when compared with conventional HPHT drilling and completion fluids such as: minimal formation damage, maintenance of additve properties at high temperatures, reduced hydraulic flow resistance, low potential for differential sticking, naturally lubricating, very low corrosion rates, biodegradable and pose little risk to the environment etc. Formate-based fluids can be applied during deep slim hole drilling, shale drilling, reservoir drilling, salt and gas hydrate formations drilling.

The laboratory research was carried out to evaluate the rheological behavior of formate-based fluids as a function of temperature. Formate-based fluids were formulated using potassium formate brine, xanthan polymer, PAC, starch and calcium carbonate. Experimental results show that potassium formate improves the thermal stability of polymers.

Kljucne rijeci: isplake na bazi formijata, kalijev formijat, visoka temperatura, svojstva fluida, busenje

Sazetak

Isplake na bazi formijata uspijesno se primjenjuju tijekom razlicitim radova u busotinama s visokim tlakom i temperaturom. One imaju nekoliko prednosti u odnosu na standardne isplake koje se koriste tijekom busenja i opremanja busotina s visokim tlakom i temperaturom, kao npr.: minimalno ostecenje formacije, ocuvanje svojstava aditiva kod visokih temperatura, smanjenje trenja, smanjenje opasnosti od diferencijalnog prihvata, poboljsana mazivost, smanjena korozivnost, biorazgradivost i neznatan utjecaj na okolis. Isplake na bazi formijata nasle su svoju primjenu tijekom izrade dubokih busotina malog promjera, busenja kroz naslage sejla, busenje kroz lezista ugljikovodika, te tijekom izrade kanala busotine kroz naslage soli i plinskih hidrata.

Provedena su laboratorijska ispitivanja kojima je utvrðena ovisnost promjene reoloskih svojstva isplaka na bazi formijata u ovisnosti o temperaturi. Isplake na bazi formijata sastojale su se od kalij formijata, xanthan polimera, polianionske celuloze, skroba i kalcijevog karbonata. Ispitivanja su pokazala da kalij formijat poboljsava temperaturnu stabilnost polimera.

Introduction

The formate salts of the formic acid have very high solubilities in water, creating dense, alkaline brines of relatively low viscosity with a range of beneficial properties, such as reduced rate of hydrolytic and oxidative degradation of many viscosifiers and fluid loss agents at high temperatures, which make them ideally suited for use as drilling and completion fluids (Downs, 1992., 1993; Howard, 1995.; Gallino, 1997.). The three monovalent formate salts considered most useful to the oil industry are sodium formate, potassium formate and cesium formate (Table 1) (Downs, 1992. 1993.).

In addition to that, they are biodegradable, have a low toxicity to aquatic organisms and display very little corrosiveness towards ferrous-based metals used in oilfield tubulars and auxiliary hardware.

Formate brines were used as the basis of low-solids drilling fluids for deep and slim hole drilling, as a drilling fluid in drilling through very plastic shales, as a high temperature reservoir drilling fluid, and as a completion and workover fluid (Abou-Sayed, 1996.; Downs 1992.; Sundermann 1996.; Gallino, 1997.; Bungert, 2000.; Gilbert, 200.; Al Otaibi et al., 2008).

The advantages of formate brines in these applications were:

* Effective hole cleaning at high downhole temperatures

* Elimination of solids sag at high downhole temperatures

* Excellent polymer stability up to 154 °C

* Minimal circulating pressure losses

* Low differential sticking potential (thin, easily removable filter cakes)

* Low ECD's in long/narrow boreholes

* Maximum power transmission to mud motors and bits

* Reduced drilling time, time spent for bit balling and time spent on reaming

* Non-hazardous

* Compatible with reservoir minerals and liquid phases (no formation damage)

* Good inhibition of formation clays (increased hole stability and reduction in wastes produced/hole volume)

* Compatible with drilling/completion hardware and elastomers (no corrosion)

* Increased ROP

* Low treatment costs during drilling

* Environmentally responsible and readily biodegradable (savings on waste disposal)

Generally, formate-based fluids can solve the problems routinely encountered with the temperature limited, calcium carbonate weighted, and water-based polymer drilling fluids such as inadequate solids suspension, poor solids transport, stuck pipe, and tight holes.

Field experience

Solids-free formate brines were introduced in practice in the early 1990 s (Downs, 1993.; Bungert et al., 2000.; Al Otaibi et al., 2008.). Formate fluids have been used in hundreds wells across the world since their comercial introduction in 1993. Table 2 presents different data colected from the published literature regarding field experience in formate based fluids application.

Laboratory testing - Fluid formulation and results

In laboratory, three fluids (marked as DIF-1, DIF-2, and DIF-3) were prepared, with 50 % w/w potassium formate and one fluid without potassium formate (marked as WBF) (Table 3). Fluid formulations shown in Table 2 contain base fluid and four components: viscosifying biopolymer, fluid loss polymers (starch and PAC) and sized calcium carbonate. A viscosifying biopolymer (xanthan gum) provides thixotropic properties and solid carrying capacity. Fluid loss polymers provide filtration control. Sized calcium carbonate is necessary as solid particulates for bridging purposes. Dilution water was necessary to decrease the base fluid density. The polymers were hydrated in the dilution water and that mixture was added to the base saturated brine. Water based fluid was chosen and tested to allow comparison of effectivity of formate based fluids.

Rheological properties at temeratures up to 160 °C (plastic viscosity, yield point, gel strenghts, index of consistency, flow index) were determined from readings of shear stress data at different shear rates obtained by using HPHT viscometer - OFITE Model 1000 and presented in the Table 4 and Figures 1 to 6 as well as API fluid loss, filter cake thickness and friction coefficient data presented in the Table 4 and Figure 7.

Rheological properties (plastic viscosity and yield point,) of water based fluid (WBF) and potassium formate based fluids decrease with increasing temperature. Potassium formate based fluid DIF 3, that contains the same amount of additives as WBF fluid shows higher values than it that means potassium formate stabilizes polymers at higher temparatures. Potassium formate based fluid (DIF-1) designed without addition of polyanionic cellulosic polymer (PAC) shows very low values of rheological properties. Increasing of PAC concentration in potassium formate based fluids (DIF-2 and DIF-3) results in higher values of plastic viscosity and yield point at same temperature.

Figure 7 presents API fluid loss, filter cake thickness and friction coefficient data. Potassium formate based fluids show lower values of API fluid loss and friction coefficient than water based fluid. Potassium formate based fluid (DIF-2) with 10 g/l PAC shows lower values of API fluid loss and friction coefficient and thiner filter cake than fluid DIF-3 prepared with higher concentration of PAC. Generally, potassium formate based fluids gave a thin filter cake of <0,5 mm in API fluid loss test.

Conclusions

The comparison of the laboratory research results shows that potassium formate based fluid DIF-3 shows better rheological and filtration properties than water based fluid, especially at higher temperatures. This fact allows to conclude that potassium formate stabilizes viscosifiers and fluid loss polymers enabling better rheological properties at higher temperatures. WBF and potassium formate based fluids without PAC (DIF-1) have inadequate rheological properties at temperatures higher than 125 °C. Generally, the most acceptable results have achieved with formate based fluid DIF-2 that contain 10 g/L PAC. The better results have not achieved by further increasing of PAC concentration (DIF-3).

Acknowledgement

This paper is based on work financed by the Croatian Ministry of Science, Education nad Sports under project 195-1951390-1394 "Rocks/Drilling Fluids Interaction Studies".

Accepted: 02.11.2008.

Received:15.07.2008.

References

References

Al Otaibi, M.B., Nasr-El-Din, H.A., Hill, A.D., (2008.): Characteristics and Removal of Filter Cake Formed by Formate-Based Drilling Mud; paper SPE 112427, presented at the 2008 SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 13- 15 February.

Bungert, D., Maikranz, S.,. Sundermann, R, Downs, J., Benton, W., Dick, M.A. (2000.): The Evolution and Application of Formate Brines in High-Temperature/High-Pressure Operations; SPE 59191, presented at 2000 IADC/SPE Drilling Conference, New Orleans, Louisiana, USA, 23-25 February.

Byrne, M., Patey, I., George, L., Downs, J., Turner, J., (2002.): Formate Brines: A Comprehensive Evaluation of Their Formation Damage Control Properties Under Realistic Reservoir Conditions; SPE 73766, presented at the SPE International Symposium and Exhibition on Formation Damage Control held in Lafayette, Louisiana, 20-21 February.

Downs, J.D., (1992.): Formate Brines: New Solutions to Deep Slim- Hole Drilling Fluid Design Problems; paper SPE 24973, presented at the European Petroleum Conference, Cannes, France, 16-18 November.

Downs, J.D., (1993): Formate Brines: Novel Drilling and Completion Fluids for Demanding Environments; paper SPE 25177, presented at the SPE International Symposium on Oilfield Chemistry, New Orleans, LA, USA, 2-5 March.

Downs, J.D., Killie, S., Whale, G.F., Inglesfield, C., (1994.): Development of Environmentally Benign Formate-Based Drilling and Completion Fluids; paper SPE 27143, presented at the Second International Conference on Health, Safety & Environment in Oil & Gas Exploration & Production, Jakarta, Indonesia, 25-27 January.

Downs J.D., Howard S.K., Carnegie A. (2005.): Improving Hydorcarbon Production Rate Through the Use of Formate Fluids - A Rewiev; SPE 97694, presented at International Improved Oil Recovery Conference in Asia Pacific, Kuala Lumpur, Malaysia, 5-6 December.

Downs, J.D., Blaszczynski, M., Turner, J., Harris, M., (2006.): Drilling and Completing Difficult HP/HT Wells With the Aid of Cesium Formate Brines - A Performance Review; paper IADC/SPE 99068, presented at the IADC/SPE Drilling Conference, Miami, Florida; USA; 21-23 February.

Gallino, G., Guarneri, A., Maglione, R., Nunzi, P., Xiao, L. (1997.): New Formulations of Potassium Acetate and Potassium Formate Polymer Muds Greatly Improved Drilling and Waste Disposal Operations in South Italy, paper SPE 37471, presented at the 1997 Production Operations Symposium, Oklahoma City, Oklahoma, 9-11 March.

Gaurina-Meñimurec, N., Tuschl, M., Simon, K. (1999): Formate Brines - Environmentally Acceptable Solution for Off-shore Drilling, Offshore mediterranean Conference - OMC99, Ravenna, 24-26 March.

Gilbert, Y., Pessala, P., Vaahtera, A., Raivio, T., (2007.): Formate Fluids and Environmental Regulations: A Global View of Benefits and Challenges; paper SPE 110891, presented at the 2007 SPE Annual Technical and Exhibition, Anaheim, California, USA, 11-14 November.

Howard S.K. (1995.): Formate Brines for Drilling and Completion: State of the Art; SPE 30498, presented at SPE Annual Techical Conference & Exhibition, Dallas, USA, 22-25 October.

Javora, P. H, Mingjie, Ke, Stevens, R.F., Berry, S.L. (2003.): The Chemistry of Formate Brines at Downhole Conditions; SPE 80211, presented at SPE International Symposium on Oilfield Chemistry, Huston, Texas, USA, 5-7 February.

Pedersen, B.K., Pedersen, E. S., Moriss, S., Constable, M. V., Vissapragada, B., Sibbit, A., Stoller, C., Almaguer, J., Evans, M., Shray, F., Grau, J., Fordham, E., Minh, C. C., Scott, H., McKeon, D. (2006.): Understanding the Effects of Cesium/Potassium Formate Fluid on Well Log Response - A Case Study of the Kristin and Kvitebjorn Fields, Offshore Norway; SPE 103067, presented at the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, U.S.A., 24-27 September.

Shaughnessy, J.M., Romo, L.A.,. Soza, R.L (2003.): Problems of Ultra-Deep High-Temperature, High-Pressure Drilling; SPE 84555, presented at the SPE Annual Technical Conference and Exhibition, Denver, Colorado, USA, 5-8 October.

Svendsen, O., Toften, J.K., Marshall, D.S., Hermansson, C.L., (1995.): Use of a Novel Drill-In/Completion Fluid Based on Potassium Formate Brine on the First Open Hole Completion in the Gullfaks Field; paper SPE/IADC 29409, presented at the 1995 SPE/IADC Drilling Conference, Amsterdam, 28 February - 2 March.

Zuvo, M., Bjornbom, E., Ellingsen, B., Buffagni, M., Kelley, A., Trannum, H.C., (2005.): High-Resolution Environmental Survey around an Exploration Well Drilled with Formate Brine in the Barents Sea, Norway; paper SPE 94477, presented at the 2005 SPE/EPA/DOE Exploration and Production Environmental Conference, Galveston, Texas, USA, 7-9 M