GEOSYNTHESIS ENGINEERING

Development and service of drilling fluid

After a break of several decades long, in Ukraine, a hydrocarbon-based cement slurry has been used anew. One of the wells operated by DTEK Naftogaz, being drilled using Witer II invert emulsion drilling mud, in the 5238 – 5472 m interval, at the temperature of 147 °C, a cement plug was successfully performed to isolation the water-saturated formation. The parameters of the hydrocarbon-based cement slurry, chosen for the cement plug and of the stone obtained from it, are presented in the table:


Tab eng

The cement plug installed in the well had sufficient strength and high insulating properties. Testing of the new cementing system was successful.

Essentially, this is the revival of the technology developed in the 1970s by V.Z. Luban and E.A. Ogolikhin under the guidance of Professor L.K. Mukhin at Moscow Institute of Petrochemical and Gas Industry named after Ivan Gubkin. However, the basis of it is a fundamentally new formulation.

IOECS-2, the new cementing system, was developed by our Company in collaboration with Techkor LLC. The main customer was DTEK Naftogaz, with the aim to apply the product in the conditions of deep horizons with abnormal pressures and temperatures.

According to the currently available data, as of today IOECS-2 is an unparalleled cementing system capable of creating a cement stone without phase inversion of the emulsion and, at the same time, corresponding to the thermobaric conditions of Ukraine.

INVERTED OIL-EMULSION CEMENT SLURRY (IOECS -2)

General information

  1. Inverted oil-emulsion cement slurry was designed for cementing casing strings and installing cement plugs in the intervals that were drilled using hydrocarbon-based drilling fluids, including AHFP zones.
  2. Inverted oil-emulsion cement slurry is an invert emulsion, whose external phase is a hydrocarbon liquid.
  3. The formation of cement stone at all stages of hardening of an oil-emulsion cement slurry in a well occurs without changing the kind of emulsion and inverting its phases
  4. Inverted oil-emulsion cement slurry is characterized by extremely low filtration loss indices comparable to the filtration of hydrocarbon-based drilling fluids.
  5. The filtrate of the inverted oil-emulsion cement slurry is hydrocarbon fluid. The presence of water in the filtrate is unacceptable. This witnesses of the decomposition of the emulsion and inversion of its phases.
  6. Stiffening of samples of inverted oil-emulsion cement slurry is carried out in a hydrocarbon fluid medium. Contact of samples with water at all stages of the formation and hardening of cement stone is unacceptable.
  7. Cement stone formation takes place in an autoclave during 3 days at constant temperature and pressure, which correspond to thermobaric conditions in the well. Minimum temperature is 100 °C, minimum pressure is 2.0 MPa.
  8. In order to prevent the contact of the formed cement stone with the moisture in the air, immediately after removal from the autoclave, the samples must be placed into a hydrocarbon liquid, where they are stored for further testing. The shelf life of the formed cement stone in a hydrocarbon medium is not limited.

ONECR2The appearance of a cementing system IOECS-2

Technical requirements towards the cement slurry and stone

In order to ensure reliable isolation and preserve productive characteristics of reservoirs, hydrocarbon-based cement slurry and the stone obtained from it must meet the following technical requirements:

  • cement slurry density: determined by the cementing program, kg/m3;
  • electrical stability of cement slurry after preparation: not less than 150 V;
  • filtration of cement slurry at the temperature of 20 ± 5 °C and a pressure drop of 0.7 MPa: not more than 6 cm3/30 min;
  • HPHT filtration of cement slurry at reservoir temperature and pressure drop of 3.5 MPa: not more than 50 cm3/30 min;
  • type of filtrate: hydrocarbon liquid, no water detected;
  • electrical stability of the cement slurry filtrate: not less than 1500 V;
  • initial setting: determined by the cementing program, hour-min;
  • final setting: determined by the cementing program, hour-min;
  • electrical stability of the cement slurry after consistometry under thermobaric conditions: not less than 150 V;
  • bending strength of a 3-day-old cement stone: not less than 1.5 MPa (hardening at a static bottomhole temperature and pressure, but not less than 110 °C and 2 MPa);
  • set strength of a 3-day cement stone: not less than 5 MPa (hardening at a static bottomhole temperature and pressure, but not less than 110 °C and 2 MPa).

OFITE
Consistometry results for IOECS-2 during 4 hours (150 оС and 80 МPа)

Industrial use of hydrocarbon-based cement slurry is possible only under the circumstances that its characteristics comply with the abovementioned technical requirements. DEVIATIONS FROM THE SPECIFIED TECHNICAL REQUIREMENTS ARE UNACCEPTABLE.

Preparation, control and application at site

  1. Inverted oil-emulsion cement slurry is prepared on the surface in the scale, necessary for the cementing.
  2. For preparation, any mixing equipment can be used to ensure stable cement invert emulsion.
  3. Measuring of technological parameters is carried out after the preparation of the inverted oil emulsion cement slurry.
  4. Sample of the inverted oil-emulsion cement slurry is taken to the laboratory, where it is divided into 4 parts:
    • The first part is used to assess the mobility of cement slurry using a consistometer in thermobaric conditions simulating downhole ones.
    • The second one is loaded into the US-1-M1 unit (or its analogue) to determine the initial and final setting time.
    • The third one is placed into an autoclave for the formation of samples-beams made of cement stone, where it remains for 3 days in thermobaric conditions simulating the downhole ones. After removing from the autoclave, the beam samples are used to determine the ultimate compressive strength of cement stone.
    • The fourth part of the cement slurry sample is used to carry out a set of tests at normal temperature (20 ± 5 °C) and determine HPHT filtration under the conditions similar to the downhole ones.
  5. The results of cement slurry and stone testing are documented in an Act.
  6. WOC duration for inverted oil-emulsion cement slurry for cementing wells is at least 3 days.

SilAbsence of dilution of the salt sample during the formation of stone out of IOECS-2

Measurement of parameters

  1. The density of the inverted oil-emulsion cement slurry.
    • Measuring instruments: hydrometer AG-1, mud balance or mud balance for determining density under pressure (OFITE code 115-00 or 100-60-Х).
    • Measurement in accordance with РД 39-00147001-773-2004, at the temperature of 20 ± 5 оС.
  2. Electrical stability of the inverted oil-emulsion cement slurry
    • Measuring Instruments: Emulsion Electrical Stability Tester (OFI TE code 131-50)
    • Measurement in accordance with РД 39-00147001-773-2004.
    • Measurement temperature is 20 ± 5 оС.
  3. Electrical stability of the filtrate of inverted oil-emulsion cement slurry
    • Measuring Instruments: Emulsion Electrical Stability Tester (OFI TE code 131-50)
    • Measurement order: to take no less than 50 ml of the filtrate, conduct the measurement in accordance with РД 39-00147001-773-2004.
    • Measurement is performed at the temperature of 20 ± 5 °C.
  4. Cement slurry filtration at the temperature of 20 ± 5 °C and pressure drop of 0,7 МPа.
    • Measuring Instruments: API filter press (OFI TE code 140-31).
    • Measurement in accordance with РД 39-00147001-773-2004.
  5. Determination of initial and final setting of the cement stone
    • The measurement is carried out at a temperature and pressure determined by the cementing program, but not less than 110 °C and 2 MPa.
  6. Determination of the strength for bending and compression of a 3-day-old cement stone.
    • Form sample-beams of 100x20x20 mm from a 3-day-old cement stone at constant pressure and temperature determined by the cementing program and corresponding to the bottomhole conditions of the well, but not less than 110 °C and 2 MPa.
    • Conduct bending strength testing of the samples.
    • Measuring instruments: testing press equipment for determining bending/ compression strength of materials.

cementHigh adhesion strength of IOECS-2 to metal. Specimen destruction occurs along the cement stone, not along the contact with the plate

Further implementation of IOECS-2 system for cementing of casing strings will ensure reliable isolation and preservation of the productive characteristics of reservoirs exposed by hydrocarbon-based drilling fluids, which in turn creates the basis for increasing the depth of drilling in search of oil and gas deposits at greater depths.