The article represents the technical peculiarities and advantages of the cementing technique with the use of foamed ceramic microspheres Kerwood^® or, shortly, foamed ceramics

The urgent task while building a well is a cement lift support following the production string in order to overlap permeable, absorbing strata and reservoirs with ensuring the normative strength of oil-well cement as well as reducing costs and time when isolating acquisition zones.

There are four main directions of relieving the oil wells mortars:

• increasing water-cement ratio
• aeration of the grouting mortar with air-gas mixtures
• use of weight light additives [1], [2]
• chemical reaction and air-entraining of components while cementing.

Finely porous foamed ceramic microspheres of the specified size 0.1 to 0.6 mm with a solid and strong shell are used as a lightweight filler.

Multifunctional foamed ceramic microspheres are produced by «STEP-Invest» Limited Liability Company in Kopeisk, Chelyabinsk region, from natural opal-cristobalite rocks according to the unique patented technology.

Appearance of foamed ceramics Kerwood^®

The filler is a light spherical granule with a dense shell and internal structure resembling a solid soap foam. This form allows granules to work as efficiently as possible in the final materials (for example, when plastering, the effect of «rolling» occurs).

Kerwood foamed ceramics ranges from 0.04 mm to 5 mm and is divided into seven standard fractions.

 

Application of foamed ceramics as a lightweight inert additive provides a number of advantages:

• one step cementation instead of the two step method;
• decrease in the specific gravity of the grout up to 1500 kg/m³ (in comparison to the light-weighted gel-cement mortar of 1650 kg/m³ and grouting mortar for a productive horizon of 1850 kg/m³) with providing the given height of the mortar lifting.

Grouting mortar obtained with Kerwood^® foamed ceramics has low density but high strength, low index of water separation, good pumpability. The cost of foamed ceramics is 3 times smaller in comparison with imported analogues.

The results of the «Tatneft» Research and Development Planning Institute laboratory’s studies of the lightweight grouting mortar with addition of foamed ceramic microspheres are presented in the Table 1.

Table 1. Physical and mechanical characteristics of the grouting mortar with the addition of foamed ceramics

Grouting mortar composition	Identifiable characteristic, unit	Conditions of the experiment	Meaning	Technical demands of the «Tatneft» LLC for the grouting mortar with lightweight foamed ceramics for productive and unproductive intervals
Grouting mortar with lightweight foamed ceramics	Density, kg/m3	atmospheric conditions	1470	within 1250–1600
	Flowability, mm	atmospheric conditions	232	not less than 200 mm
	Water separation, ml	atmospheric conditions	1.1	not more than 5 ml
	Strength of a stone for bending/ compression in 48 hours, MPa	atmospheric conditions	1.7/4.6	not less than 1.4/4.0 MPa
	Consistency, min-Bc	T = 30 °C, P = 30 MPa	204–30 225–45	Not less than 225 at T = 30 °C, P = 25 MPa
	Setting time, start/end, hr-min	atmospheric conditions	7:00–10:20	—
	Consistency, min-Bc	atmospheric conditions	312–7	—

Grouting mortar obtained with the addition of foamed ceramics can improve the quality of fastening and maintenance reliability of wells. The possibility of high quality cementing process with fiberglass production string is acknowledged.

Cementing of four wells with the lightweight grouting mortar with addition of foamed ceramic microspheres (Table 2) while cementing production strings in the «Tatneft» Research and Development Planning Institute under the program of experimental-industrial works.

Table 2. Results of the program of industrial experimental process using the grouting mortar with foamed ceramics

No. of wells Date of cementation	Company	Depth, m/∅ eh, mm	Information according to the results of the cemented wells	Density of the relieved grouting mortar cement, kg/m3
№ 1 06.06.17	«Yamashneft» Leninogorsk drilling company	1468/114	Wells are handed over in operation and have obtained the planned production. The quality of cementing corresponds to normative indicators in the «Tatneft» LLC	1570
№ 2 13.09.17	«Prikamneft» Leninogorsk drilling company	1577/168		1510
№ 3 27.08.17	«Yamashneft» Bavly drilling company	892.5/90.2 fiberglass casing pipes		1570
№ 4 28.10.17	«Yamashneft» Nurlat drilling company	932/90.2 fiberglass casing pipes		1540

Average density of the lightweight grouting mortar with addition of foamed ceramic microspheres was 1550 kg/m³ according to results of cementing of 4 wells.

There were no negative remarks on technological parameters relating to the lightweight cement.

The confirmatory result of laboratory tests on the ultrasonic cement analyzer (UСA) and a consistometer is presented at diagrams (Pictures 4 and 5).

The process of experimental-industrial works on four wells, according to the program of industrial experimental works, was completed successfully. The quality of cementation corresponds to the normative indicators in the «Tatneft» Research and Development Planning Institute.

Cementing of the production string of fiberglass casing pipes by «Tatneft-Presscomposit» Limited Liability Company was performed at two wells with the help of the lightweight oil-well cement with a density of 1540 – 1570 kg/m³ with the addition of foamed ceramics used for relieving the weight of the grouting mortar to prevent the surfacing of the production string made of fiberglass casing pipes.

During the program of industrial experimental process and analysis of the obtained results the technological and economic efficiency of the technology was revealed.

1. Ensuring the lifting of cement to the mouth in one stage in contrast to the basic technology of cementing under identical mining and geological conditions.
2. Reducing the costs for the liquidation of acquisition zones:
   • to prepare the wellbore for fastening, aggradation, in connection with the reduction of insulation requirements to absorption zones due to a decrease in the density of oil-well cement;
   • exclusion of the step cementing clutch and additional waiting time for solidification of the cement: 6–8 hours, drilling of the step cementing clutch and crimping the production string, increasing the construction period of the well at least by 12 hours.
3. Improving the quality of fastening wells due to the reduction of water loss, increase in the strength of the cement stone with foamed ceramics. Increase in reinforcement reduces the risk of behind-the-casing circulation and increases operational reliability of wells.
4. There is a possibility of reducing the waiting time for solidification of the cement using foamed ceramics from 48 to 24 hours.
5. Replacement of two compounds of oil well cement to the productive and overproductive horizons of one composition, corresponding to the strength of the performance indicators.
6. Approbation of cementing of fiberglass casing with lightweight oil-well cement was carried out to exclude surfacing of casing and quality assessment by standard geophysical methods of research.
7. An effective field of application of the cementing technology using foamed ceramics was determined and recommended for industrial use in the «Tatneft» PJSC.

Conclusions

• The cost of foamed ceramics is 3 times smaller in comparison with imported analogues.
• The grouting mortar obtained with the addition of foamed ceramics increases fastening and operational reliability of the wells.
• The possibility of carrying out high quality cementing process from fiberglass production string is confirmed.
• The grouting mortar with Kerwood^® foamed ceramics has low density but high strength, low water drainage, good pumpability.

Referencies

1. Kateyev R. I., Amerkhanova S. I., Zaripov A. M., Gazizov M. G., Latypova D. V. [Lightening additive for grouting mortars] [Construction of oil and gas wells on land and at sea], 2014, no. 11, pp. 47–49.
2. Kateyev R. I., Amerkhanova S. I., Zaripov M. G., Gazizov A. M., Latypova D. V. [Foamglass as an easy-to-use additive for grouting mortars] [Collection of scientific papers of TatNIPIneft], Moscow, «Oil economy» Publ., 2014, Vyp. 82, pp. 232–234.
3. Zaripov I. M., Ishakov A. R., Zaripov A. M., Gazizov M. G., Ratnikov K. A., Makhmutov I. Kh. [Construction and repair of wells of PJSC «Tatneft» using casing strings made of fiberglass casing pipes] [Collection of scientific works «TatNIPIneft»], Moscow, «Oil economy» Publ., 2017, Vyp. 85, pp. 302–307.