Testing Geothermal-Well Cements:

High Temperature, High Pressure,

and Fluid Handling Facility

J '

Ralph F. Krause, Jr. Edwin R. Fuller, Jr.

Fracture and Deformation Division

Center for Materials Science

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

F

October 1 979

Interim Report

Issued July 1 980

for

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! 80-2099-3

Jkin of Geothermal Energy

[ Department of Energy

hington, DC 20461

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MATIONAL BUUAD

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LIBRARY

NBSIR 80-2099-3 1 9 1980

TESTING GEOTHERMAL-WELL CEMENTS:

HIGH TEMPERATURE, HIGH PRESSURE,

AND FLUID HANDLING FACILITY

Ralph F. Krause, Jr. Edwin R. Fuller, Jr.

Fracture and Deformation Division

Center for Materials Science

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

October 1 979

Interim Report

Issued July 1980

Prepared for

Division of Geothermal Energy

U.S. Department of Energy

Washington, DC 20461

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technoiogy. and Innovation

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NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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Abstract

Construction of a high temperature, high pressure, and fluid handling

facility, which includes four pressure vessels of Hastelloy alloy C, has

been completed. The facility allows set cements to be exposed to simulated

geothermal fluids at pressures up to 60 MPa (8700 psi) and at temperatures

up to 400 °C. Two of these pressure vessels are equipped for measuring

either* the shear-bond strength of the cement-steel interface or the

cement permeability to water at elevated temperatures and pressures. In

addition, there is a fifth pressure vessel of stainless steel 316 which

can be used for set-curing cements in molds under water at pressures up

to 21 MPa (3000 psi) and at temperatures up to 340 ^C.

Introduction

The facility which is described below was built as part of the

development of a laboratory testing technique for evaluation of certain

physical properties of set cements which are candidates for use in

finishing geothermal wells. Selection of a cement for cementing a steel

pipe in a well is particularly important to avoid well failure due to

cement degradation. Long term operation of a well is necessary because

a major cost of producing geothermal energy is in the drilling of the

well. To provide a broad base for identifying improved cements, new

formulations of cements have been requested from a number of sources.

The laboratory testing technique will provide data on these new cements

after they have been set in molds and then exposed to simulated geothermal

conditions for extended periods. Properties to be measured include

shear-bond strength of the cement-steel interface, permeability to water.

1
splitting tensile strength, and compressive strength. Having this data,

governmental and industrial users can assess these cements as to whether

they satisfy certain requirements prior to costly field tests.

The practice for testing geothermal -wel 1 cements is described in

detail elsewhere [1]. The present report describes the high pressure,

high temperature, and fluid handling systems that have recently been

installed. Also included is the tentative arrangement for measuring

shear-bond strength and permeability at elevated temperatures and pressures.

High Pressure Systan

A schematic sketch of the high pressure system is shown in figure

1. It includes four high pressure vessels of Hastelloy alloy C-276.

Each of these pressure vessels has an inside diameter of 50 mm, an

inside length of 250 mm, and three ports, two for the entrance and

discharge of fluids, and one for a sheathed thermocouple (not shown in

figure 1). Each pressure vessel is mounted in a separate, opened back

module (76 cm, 76 cm, 122 cm high). Steel panels (3 mm thick) which are

bolted to steel framing channel (4.1 cm square) form the sides of these

four modules. Fluid flow to the pressure vessels is controlled by high

pressure valves of Hastelloy alloy C-276 which are mounted behind and

whose stems protrude through the front panels of the modules. Pressure

is indicated by bourdon gauges which have monel coils and sockets, and

over-pressure is limited by safety rupture discs of Hastelloy alloy C.

High pressure monel tubing (2.1 mm inside diamter) directly joins the

vessels and their accessories through coned and threaded high pressure

fittings. These pressure vessels will be used to expose set cements to

simulated geothermal fluids at pressures up to 60 MPa (8700 psi).

- 2 -
A fifth pressure vessel of stainless steel 316 (127 nm inside

diameter, 300 mm inside length) is mounted on a nearby stand and is

equipped with a packed stirrer, an internal cooling coil, a bourdon

pressure gauge, and a safety rupture disc. This vessel will be used to

set-cure cements in molds under water at pressures up to 21 MPa (3000 psi).

A high pressure metering pump provides pressures up to 69 MPa

(10,000 psi), or alternatively, a source of compressed nitrogen, up to

40 MPa (5800 psi). This pump delivers a fluid flow (adjustable up to 13

ml /min) through a Hastelloy alloy C-4 pump head. The output of the pump

can be maintained at a constant pressure since it is powered by an air

motor that drives a geared plunger against a tantalum diaphragm in the

pump head.

A special feature of the high pressure system is the pair of capacitancesensing, pressure transducers of stainless steel 17-4 PH, which will be

operated at room temperature. These transducers respond linearly within

jjO.l percent over the pressure range between zero and 69 MPa (10,000 psi)

and can be read to a precision within 3 kPa (0.4 psi). They will be

used for in situ measurements of permeability and shear-bond strength at

elevated temperatures and pressures.

Hastelloy alloy C and monel were deliberately chosen for fabrication

of most of the high pressure system in order to avoid generalized surface

corrosion and pitting stress corrosion which many metals incur upon

exposure to salt solutions, especially at high temperatures. Unfortunately,

neither Hastelloy alloy C nor monel was easily available for fabrication

of the pressure transducers. Stainless steel 17-4 PH generally has good

resistance to pitting stress corrosion at room temperature, and possible

corrosion can be limited by the use of oil to separate it from the salt

- 3 -

solutions.
High. Tanperature System

Five tube furnaces, which are nichrome wire-wound, have been vertically

mounted to heat the high pressure vessels individually. One furnace

(159 mm inside diameter, 305 mm height) has opened ends and a single

heater-zone; it annularly surrounds only the body of the stainless steel

pressure vessel while the entire cap and bottom end of this vessel are

exposed to room air. This situation poses no serious problem as long as

the contents of the vessel are stirred.

The other four 'furnaces (102 nm inside diameter, 635 mm height) are

the split-tube type; each of these has two heater-zones and thermally

insulated end plugs. During operation, a split- tube furnace completely

encloses a Hastelloy pressure vessel, which is supported upright on a

thin-walled stainless steel tube (76 mm diameter) that is packed inside

with thermal insulation. The main heater-zone (305 mm length) of a

split-tube furnace surrounds the vessel body while the other heater-zone

(76 mm length) surrounds the vessel cap. The power to the cap-zone is

adjustable as a manually variable proportion of that to the body-zone.

These Hastelloy vessels- can be cooled about 3 °C/min by compressed-air

flow through the furnace interior.

Each of the five furnaces is electrically powered (208 V AC, 3150 W)

by a separate temperature controller. The difference between thermocouple

input and set point signals is conditioned by proportional mode of

control with automatic reset and automatic rate to drive time-based

triac output. When the furnaces commence heating the pressure vessels

from room temperature, full power provides a heating rate of about

3 °C/min. The controllers maintain a final operating temperature within

+1 °C. The maximum operating temperature is 340 °C for the stainless

steel vessel and 400 °C for the Hastelloy vessels although the furnaces

are capable of much higher temperatures.

- 4 -
Chromel-alumel thermocouples are used to indicate temperature on a

digital voltmeter which is calibrated to read within +1 °C. Each Hastelloy

pressure vessel is equipped with 3 thermocouples: one junction being

located about halfway down along the inside vessel wall; another, around

the middle of the outside of the vessel cap; and a third, around the

middle of the outside of the vessel body. The inside thermocouple is

sheathed in a Hastelloy tube (1.6 mm outside diameter) while the outside

thermocouples are sheathed in stainless steel tubes of the same size.

The stainless steel pressure vessel is equipped with one thermocouple

which is inserted down a thermo-well (3 mm inside diameter) inside the

vessel

.

Fluid Handling System

Three stainless steel cylinders serve as reservoirs for fluids of

differing compositions. As figure 1 shows, manipulation of stainless

steel valves can direct these fluids through a common manifold to any of

the high pressure vessels. Besides distilled water, the fluids we plan

to use are light and heavy concentrations of mixed salts (NaC£, KC£,

CaC£

2

» and NaHCO^) in aqueous solutions [1]. A mechanical vacuum pump

is attached to evacuate the reservoir cylinders as well as the high

pressure vessels before introduction of the fluids. Either salt solution

can be equilibrated with a given partial pressure of carbon dioxide to

prepare a simulated geothermal fluid, whether it is in its reservoir or

in a high pressure vessel.

A pH meter is available to monitor the acidity of fluids. A glass

measuring electrode and a reference electrode are mounted in a stainless

steel chamber in line between the reservoir cylinders and the high

- 5 -
pressure metering pump. These electrodes can be used to make pH measurements of the buffered carbonic acid solutions at pressures up to 1 MPa

(145 psi).

Arrangement for Measuring Permeability

and Shear-Bond Strength

As figure 1 shows, either of two Hastelloy pressure vessels can be

connected to the pair of pressure transducers for conducting a test of

cement permeability to water or a test of the shear-bond strength of the

cement-steel interface. These Hastelloy vessels will be used for in

situ measurements at elevated temperatures and pressures. Another

vessel of stainless steel, not heretofore discussed, can be connected to

one pressure transducer and will be used only for permeability measurements

at room pressure and room temperature.

Using the appropriate practice [1], specimens of cement for either

test are set-cured in a mold as shown in figure 2. However, those

specimens which are designated for the shear-bond strength test are

molded to encase a smooth steel rod (10 mm diameter, 28 mm length) which

is centered by recessed cover plates at both ends of the mold. A commercially

available one-inch-pipe hex nipple of stainless steel 316 (22 mm inside

diameter, 57 mm length) was modified to serve as the mold. The nipple

was sawed in half, and the inside diameter of the resulting pieces was

tapered in a conical fashion such that the opening at the pipe threaded

end is about 5 percent larger than the opening at the hex end. Thus,

when pressure is applied to the specimen at the pipe threaded end, the

specimen tends to make a better seal with the mold.

6
When measurements are to be made at elevated temperatures and

pressures, the mold of set cement is installed within a Hastelloy pressure

vessel to make two concentric chambers. The conical plug or ring of set

cement serves as the weakest partition between these two chambers. The

threaded end of the mold is fitted with teflon pipe sealant into a hex

reducing coupling which is attached to the underside of the head of the

pressure vessel by stainless steel tubing (4.6 mm inside diameter). The

coupling assembly is installed inside the pressure vessel, and valves

are opened to make the two chambers common initially. After room air is

evacuated, the vessel is filled with distilled water and brought to the

ambient temperature and pressure of the measurement, using a furnace and

high pressure metering pump as needed. Prior to conducting a test, the

two chambers are closed off from each other except for the cement partition

While one chamber is isolated, a pressure difference is applied across

the cement specimen.

The details for calculation of permeability and shear-bond strength

are given elsewhere [1]. In brief, the permeability is calculated from

the decline of the pressure difference as a function of time after both

chambers have been isolated. The shear-bond strength, however, is

calculated from the maximum pressure difference which is required to

displace the smooth steel rod.

Reference

[1] R. F. Krause, Jr. and E. R. Fuller, Jr., "Testing Geothermal -Well

Conents: Standard Practice," NBSIR 80-2099-2, National Bureau of

Standards, Washington, D.C., Interim Report, July 1979.

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Figure 2. Cement specimen mold and holder for permeability and shear-bond

strength tests: a_ specimen of set cement (23 mm lower outside diameter,

24 mm upper outside diameter, 25 mm height); ^ smooth steel rod (10 mm outside diameter, 28 mm length) installed only for shear-bond strength test;

c_ stainless steel 316 mold for cement specimen; and d stainless steel

316 hex reducing coupling (1 inch NPT to 1/4 inch NPT) .
NBS-114A (REV. 9-76)

4, TITLE AND SUBTITLE

ESTING GEOTHERMAL-WELL CEMENTS

High Temperature, High Pressure, and Fluid Handling Facility

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. 80-2099-3

5. Publication Date July 1980

7. AUTHOR(S)

Ralph F. Krause, Jr. and Edwin R. Fuller, Jr.

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No. FA77-A-01-6010

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fSfraer, city, state, ziP)

.Division of Geothermal Energy

U.S. Department of Energy

Washington, D.C. 20461

13. Type of Report & Perio(j Covered October 1979, Interim

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or teea (actual aummary of moat aighificant information. If document includea a aignilicant bibliography or

literature survey, mention it here.) Construction of a high temperature, high pressure, and fluid handling facility,

which includes four pressure vessels of Hastelloy alloy C,has been completed. The

facility allows set cements to be exposed to simulated geothermal fluids at pressures

up to 60 MPa (8700 psi) and at temperatures up to 400 °C. Two of these pressure vessels

are equipped for measuring either the shear-bond strength of the cement-steel interface

or the cement permeability to water at elevated temperatures and pressures. In addition

there is a fifth pressure vessel of stainless steel 316 which can be used for set-curing

cements in molds under water at pressures up to 21 MPa (3000 psi) and at temperatures

up to 340 °C.

17. KEY WORDS Csix to twelve entriea; alphabetical order; capitalize only the firat letter of the firat key word unleaa a proper name;

aeparated by aemicolona)

Geothermal -well cements; high temperature furnace; high pressure vessel; permeability;

shear-bond strength; simulated geothermal fluids.

18. AVAILABILITY ^Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Sup. of Doc., U.S. Government Printing Office, Wasiiington, DC

20402, SD Stock No. SN003-003- Rn Order From National Technical Information Service (NTIS), Springfield,

VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

12

22. Price

$5.00

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