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Local Substitute for Silica Flour In High

Temperature High Pressure Enivronments

P. N. Onwuachi-Iheagwara

Abstract— This paper centered on the development of a local substitute for silica flour. This was undertaken with the objectives of examining common indigenous materials to ascertain, if any may be a suitable replacement; thus breaking the reliance on imported Silic a flour in Nigeria.

Sand; a common, cheap and readily available siliceous material, were collected randomly from the 3 senatorial districts of Delta state and Benin City. These sands were subjected to photomicrographic and grain size analyses. Based on the results, the Ughelli sands and the Benin sands were selected for in-depth investigation of early strength development and spectrometric study by infra-red, X-ray diffusion and X-ray fluorescence. 432 cements slurries were prepared with various proportions of API grade G cement, silica flour, Ughelli and Benin sands. These slurries were cured from 30 minutes to 120 minutes and their compressive strength determined at elevated pressure (5,000 to 10,000 psi) and temperature (200 to 350 degree Fahrenheit) conditions.

The investigation among other things studied the effect of a gradual substitution of indigenous sands for silica flour, traditionally used by the Petroleum Industry in Nigeria. Silica content in Ughelli sand is greater than 50%.Ughelli sands was observed to be suitable as a replacement for Silica flour (95%silica) at 60% substitution. It can therefore, be used for silicaceous enrichments of cements for deep Niger Delta oil field wells. These slurries were capable of withstanding pressure up to 9,500 psi and temperatures of 250 degrees Fahrenheit. Further research is recommended to factor –in the effect of the corrosive brine and waters at depths.

Index Terms—Niger Delta, Silica Flour, Ughelli sand

1 INTRODUCTION

——————————  ——————————
HIS is a study on the effect(s) of elevated pressures (5,000 to 10,000 psi) and temperatures (200 to 350 degrees Fahr- enheit) on API grade G cement –silica flour systems. It centered on the replacement of the silica flour with an indige- nous Nigerian material. For this investigation the following
method was adapted:

2 METHODOLOGY

2.1 Sampling Technique

After an extensive literature review on the fatigue perfor- mance of cement [1],[2],[3] and the Nigerian high pressure, high temperature scenario [4],[5]; a sampling technique was selected for the investigation; this involved an initial survey by random sampling. A total of nine sands were randomly collected from the 3 senatorial districts of Delta State (seven
samples) and Benin City (two samples). These samples were subjected to photomicrographic and grain size analyses. (Ta- ble 1)

2.2 Photomicrography Studies

Thin-sections were produced from the sands. Photomicro-
graph was made from the thin sections. These were examined
under cross polarized and plane polarized light to reveal the mineralogical make-up of the sands as shown in the appendix. (Figures 1 to 9)

2.3 Grain Size Analyses

Grain size analyses were done to determine the particle size
distribution; as the reactivity of any substance is partially de-
pendent on the respective sizes of the reacting species. The
logarithmic Udden–Wentworth grade scale was used in order
to place equal emphasis on small differences in fine particles
and larger differences in coarse particles. [6], [7] Results were analysed with grain size statistics software GRADISTAT [8] (Figures 10-18).
Based on the results of these preliminary investigations, the Ughelli and Benin sands were selected for further investiga- tion at elevated pressure-temperature conditions for strength development and spectrometry study. (Figures 19-22), [9], [10] XR-D of Benin (Figure 19) and Ughelli sands (Figure 20) were compared.The bond structure of these sands were also ana- lysed and compared with Silica flour , normally used in Nige- ria to prevent cement retrogression.

3 SAMPLES PREPARATION

Cement slurries were prepared from API grade G, silica flour and sands in various proportions. The sands were used to gradually substitute for the silica flour. The prepared ce- ment slurry specimen was placed in the mould of known cross-sectional area and cured for 30 -120 minutes before strength development at elevated conditions were investigat- ed.

4 INVESTIGATION AT ELEVATED CONDITIONS

The behavoiur of the cement slurries in high pressure, high temperature environment was created in the laboratory to mimic (simulate) the conditions at depth. A device was de- signed to supply a regulated quantity of heat via a heating element. Heat supply was synchronized via a regulator. Be- cause of the high temperature involved, temperature meas- urements were done using a thermocouple, [11] By simultane- ously subjecting the cement slurries to the effect of the Univer-

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sal Compression Tester (to generate the necessary pressure) and the heating device, a high pressure, high temperature en- vironment was mimicked (simulated).

4.1 Compressive Strength Determination at Elevated Pressure

(s) and Temperature(s)

Six different types of cement slurries were prepared, using
API grade G cement, Silica Flour, Benin sands, Ughelli sands in various proportions. Slurries of Neat API grade G cements
and Ordinary Portland cement were prepared as “controls” and used to determine cements’ response in the absence of all additives. Pressure readings were incremented by a factor of
1,000psi while the temperature readings were incremented by
50 0F. A total of 432 readings were taken.
This paper would consider data for the Ughelli sands anal-
ysis only (Table 1).

Table 1: Compressive Strength Analysis for 30 minutes curing time
Only a subset of these readings would be considered in this paper. The readings for a curing time of 30 minutes were ana- lyzed as the development of early strength is crucial for casing placement, competence and the economy. (Figure 23)

Table 2: List of Sands investigated

5 SPECTROMETRY EXAMINATIONS

Spectrometric investigations were undertaken. This in- volves infra-red analysis, XR-D. (Figures 10 to 13)

Figure 19 XR-D of Benin Sand
The spectrometry examinations revealed the chemical compo-
sition and confirm the provenance as suggested from the grain
size analysis. Samples were prepared for examination by first
crushing and pulverizing with an electric crusher for 60 se-

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conds using the Herzog gyro-mill (Simatic C7-621). Pellets were prepared from the pulverized samples; first by grinding
20 grams of each sample with 0.4 g stearic acids for 60 se- conds. After each grinding the Gyro mill was cleaned to avoid contamination; a binding agent was prepared using stearic acid and the Herzog pelletizing equipment was used to press the sample to a pressure of 200KN for 60 seconds, and form pellets. These 2mm pellets were added into a sample holder of the X-ray equipment (Philips PW-166) for analysis.

Figure 20 XR-D of Ughelli Sand
Figure 21 IR- of Silica Flour

6 CONCLUSIONS

The following are the conclusion from the study:
1. The results of the study showed that the Ughelli sands can be used as an acceptable substitute for the expensive imported Halliburton Silica flour within the temperature-pressure conditions studied.
2. The variances in all the slurries made with Ughelli sands were observed to be 0.1.
3. Among all the sands examined, the Ughelli sands showed the best promise for use in high pressure, high temperature environment.
4. The more finely grinded the Ughelli sands were the larger the surface area and the quicker the reaction.
5. Benin City sands with a lower SiO4 content if to be used in high pressure, high temperature terrain

would require a greater amount of silica flour than the Ughelli sands per weight of API grade G cement used.
6. It was observed that at constant composition and cur- ing time, the effects of change in temperature on compressive strength were not pronounced at the temperature pressure range of investigation (200-350 degrees Fahrenheit and 5,000 to 10,000 psi) when compared to the effect of increasing curing time ( from 30 minutes to 60 minutes) at constant composi- tion.

7. This study among other things identified the use of indigenous sands for siliceous enrichments of high pressure, high temperature oilfield cement slurries for Niger Delta wells.

REFERENCES

[1] Al-Suwaidi, A .S, A new cement sealant system for long-term zonal isolation for Khuff gas wells in Abu Dhabi, Paper SPE 117116. Presented at the Interna- tional Petroleum Exhibition and Conference, Abu Dhabi, U.A.E., (2008) 3-6
[2] Barron A (2010), Hydration of Portland Cement, http://creativecommons//licenses /by//2:0/
[3] Iverson B, Maxson J, Strength retrogression in cement under high temperature conditions, proceeding: thir- ty-fifth Workshop on Geothermal Reservoir Engineer- ing Stratford University, California, February 1-3 2010
[4] Department of Energy , “Application for consent to drill or re-enter high pressure high bottomhole tem- perature exploration and appraisal wells” Cson 11” Continental shelf operation Notice No 59, Department of Energy , London May (1990).
[5] Eni , Integrated drilling and logging program ap- proach in HPHT environment: successful drilling of deepwater Oberan field, Nigeria, proceeding: Pe- trotech conference – 2010, October 31 – November 03,
2010, Delhi, India
[6] Udden, J A., Mechanical composition of clastic sedi- ments. Bulletin of the Geological Society of America Vol. 2 (1914) 655–744
[7] Wentworth C. K , A scale of grade and class terms for clastic sediments. Journal of Geology Vol. 30 (1922)
377–392
[8] Blott S. J. and Pye K., Gradistat: a grain size distribu-
tion and statistics, Earth Surface Processes and Land-
forms .Earth Surf. Process. Landforms 26,(2001) 1237–
1248 2001
[9] Onwuachi-Iheagwara, P.N. and Idigbe, K. I. (a).
Comparative analysis of two indigenous Nigerian
sands. Advances in Applied Science Research, Vol 4:
3: (2013) 80-85
[10] Onwuachi-Iheagwara P.N. & K. I. Idigbe (b). The ef-
fects of increasing temperature and pressure on ce-
ment slurries treated with Ughelli sands. Internation-
al Journal of Science and Technology , (2013) 41-46

[11] Onwuachi-Iheagwara P.N., K. I. Idigbe & Olafuyi O.

A. (c) ; A methodology for the investigation of ce-
http://www.ijser.org

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ment retrogression in HP HT environments, Journal of the Nigerian Association of Mathematical Physics, Vol 25 2 (2013) 171-177

APPENDICES

Figure 7 Sands007 under plane and cross polarized light.

Figure 1 Sand001 under plane and cross polarized light.

Figure 8 Sands008 under plane and polarized light. Figure 2 Sand002 under plane and cross polarized light

Figure 9 Sands009 under plane and cross polarized light.

Figure 3 Sands 003 under plane and cross polarized light

Figure 4 Sands004 under plane and cross polarized light.

Figure 5 Sands005 under plane and cross polarized light

Figure 6 Sands006 under plane and cross poloarized light.
Figure 10 Grain size analyses for sands001

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Figure 11 Grain size analyses for sands002

Figure 12 Grain size analyses for sands003

Figure 13 Grain size analyses for sands004
Figure 14 Grain size analyses for sands005

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Figure 15 Grain size analyses for sands006
Figure 16 Grain size analyses for sands007
Figure 17 Grain size analyses for sands008

Figure 18 Grain size analyses for sands009