An Assessment Of Gravel Packing Methods Used In The Petroleum Industry
The completion of the gravel pad is simply a downhole filter designed to prevent the production of formation fines. It involves the placement of gravel on a perforated gap in the annular space of the screen casing and in the perforation tunnel to prevent the formation of fines and formation sands. However, an inaccurate determination of the size of the ballast packaging could lead to a sandblast that could affect the technical and economic aspects of the production. It is the overall goal of this project to identify ways to selectively select appropriate gravel block sizes from sieved formation sands.
Analysis to achieve optimal sand control for maximum production without sacrificing production of hard products. The method adopted for this project is the sieve analysis and sucier correlation. The results from this study showed that technically, sand production declined from 40pptb obtained from sand cut analysis of oil sample obtained from wireline formation tester to an average of 3.5pptb after installation of IGP; technically, oil production rose from 400bbl/day from drill stem test (DST) carried out before installation of IGP to an average of 858.5bbl/day after installation; and finally the economical observation showed that there was drastic reduction in well cleaning cost, work over operation cost, sand treatment and depositional cost.
Many reservoirs are comprised of relatively young sediments, which are so poorly consolidated that sand will be produced along with the reservoir fluids unless the production rate is reduced significantly. Sand production leads to many numerous production problems including erosion of down hole tubular, valves, fitting and surface flow lines, collapsed casing because of lack of formation support. Thus a means to eliminate sand production without greatly limiting production rates is desirable.
Sand production can be controlled using different methods but the method of utmost importance to this project is the mechanical method which basically involves the use of gravel pack (GRAVEL PACKING).
This method is considered the oldest and most effective sand control mechanism. It is simply a down hole filter designed to prevent the production of unwanted sands which involves the placement of gravel across a perforated interval in the sand screen annulus and also in the perforation tunnel to prevent the influx of sand.
Inaccurate determination of gravel pack size, could lead to sand influx which could be detrimental to both the technical and economic aspect of production which is the overall objective of this project aimed at identifying means to selectively select appropriate gravel pack sizes from formation sands produced through sieve analysis to meet optimum sand control for maximum production without any detrimental effect to production hard wares.
In a gravel pack completion, sand that is larger than the average formation sand grain is placed between the formation and a screen or slotted liner with the aim of retaining most of the formation sand, but letting very fine particles through it and be produced.
The two most common types of gravel pack completion are the inside casing gravel packing or internal gravel packing (IGP) and underreamed gravel pack or external gravel pack (EGP). The underreamed casing gravel pack provides better conductivity through the gravel but is limited to single zone completion.
1.1 Aims And Objectives
This project is aimed at
- To study the various types of gravel packing methods used in the petroleum industry.
- To analyze sieve analysis data of formation sands gotten from OBEN13L in other to determine the appropriate gravel pack size used.
- To make conclusions on the state of OBEN WELL 13L on the basis of sieve data analysis and give possible recommendations.
1.2 Scope And Limitation
The scope of this project is limited to the mechanical method of sand control with more emphasis on the sieve analysis of formation sands gotten from OBEN13L.
The method to be adopted for this project is the use of sieve analysis and sucier correlation to determine the gravel pack size to be used for OBEN WELL 13 with formation sands gotten from the case study as mentioned above and useful information gotten from the internet, textbooks, petroleum journals.
This method simply involves collecting core samples and running them through different sieves with different opening sizes, usually sieves with larger openings at the top and sieves of smaller opening at the bottom and plotting each weight retained on each sieve against the sieve opening size to determine the average formation sand size which is used to find accurate gravel size using sucier correlation.
Conclusion And Recommendations
From analysis of laboratory work done on OBEN 13L (E70Asands), results showed that installation of IGP was highly advantageous to both the technical and economic aspect of production.
The well was monitored for seven months after the installation of IGP and the following observations were made.
- Technically, sand production declined from 40pptb obtained from sand cut analysis of oil sample obtained from wireline formation tester to an average of 3.5pptb after installation of IGP.
- Technically, oil production rose from 400bbl/day from drill stem test (DST) carried out before installation of IGP to an average of 858.5bbl/day after installation.
- The economical observation showed that there was drastic reduction in well cleaning cost, work over operation cost, sand treatment and depositional cost.
- Also it was observed economically that pay back time on investment was reasonable for treatment cost and thus the gain per day and annual cash flow increased drastically.
The above observations stated show that installation of IGP at initial completion, which involves accurate determination of gravel pack size using sucier correlation should be encouraged and have a wide use in future sand control practices in reservoirs where the probability of sand production is high. Thus it was shown that sand production was successfully mitigated in OBEN 13L sands using a 14 U.S mesh size or in inch equivalent 0.0498 inch gravel pack size.
Prior to results gotten from OBEN13L, it was shown that installation of IGP at initial completion which involves accurate determination of gravel pack size using sieve analysis should be highly encouraged and have a wide spread application in future sand control practices in reservoirs where probability of sand production is high, for its ability to prevent sand influx as done in OBEN WELL 13L as shown from results obtained. Though the gravel pack design was successful but had a few drawbacks which are presented below:
- Presence of mud in side wall core samples which was mistaken for formation material.
- Localized crushing of sand grains, producing broken sand grains and generating more fine grains which might not be representative to the formation sand size, giving imprecise result.
With these drawback observed, a more corrective approach to mitigate these draw backs should be undertaken by the following:
- Using bland coring fluids to prevent invasion into the core fluids
- The use of conventional coring method with bland coring fluids to give representative sample of the formation.
Though, this could not be done due to financial constraint and equipment availability.
I strongly recommend that after every gravel pack operation, gravel pack evaluation should be done using unfocused gamma ray density logs to locate the top of the gravel pack section and also to detect voids in the gravel pack by measuring density of materials in the region of well completion.
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