APPLICATION OF ENGINEERED WATER BASE DIF FOR OHGP
COMPLETION
L. Martini, G. Ripa, D. Pellicanò, Eni U&T Services, G. Carmelo, Petrobel, I. Zaky,H.
Shabaka,S. D’angelo Halliburton
.
This paper was presented at the 13th Offshore Mediterranean Conference and Exhibition in Ravenna, Italy, March 29-31, 2017. It was
selected for presentation by OMC 2017 Programme Committee following review of information contained in the abstract submitted by
the author(s). The Paper as presented at OMC 2017 has not been reviewed by the Programme Committee.
ABSTRACT
To drill and complete high efficiency and trouble free well is nowadays the most valuable way to
carry out a development plan. Drilling progress and production rates monitored on a daily basis by
the highest authority to ensure production schedule is uninterrupted or unhindered. With this in
mind, it is critical to ensure that the Drilling fluid is engineered to address the drilling challenges
and ensure minimum damage to the producing formation to maximize the production rates.
The main target for the Drill- In fluid is to drill through the highly reactive interbedded Kafr el Sheikh
shale and into the sand gas reservoir of the Egyptian concession with water base fluid while
minimizing whole fluid losses to the formation and achieve zero skin factor. With known sand
permeability and shale reactivity, the fluid is engineered to both effectively bridge the sand and at
the same time provide the required inhibition.
INTRODUCTION
Shale samples and sand data were collected for comprehensive lab testing to ensure the right
inhibition, encapsulation and lubrication as required.
Shale reactivity required additional
encapsulation and inhibition. After utilizing proprietary software to design the bridging package
particle size distribution, the resulting outputs where tested and optimized in the lab. Furthermore,
the final fluid formulation at 1.25 SG was tested in a core flood study whereby the reservoir
downhole conditions such as overburden and differential pressures, flow regime and permeability
were simulated. Therefore some efforts have been made in the lab to find out the best biopolymer
to viscosify the KCl brine selected to achieve 1.05 kg/l and to optimise the particle size distribution
of the calcium carbonate in order to promote the creation of a very thin and tight filter cake that
would minimize differential sticking tendencies and be resistant to erosion during the gravel pack
process. Through the use of core flooding tests, this drill-in fluid showed a very good recovery of
the permeability and the formation of a filter cake with excellent fluid loss control performance.
In the field, all drilling and completion phases proceeded as planned and no fluid losses were
recorded while drilling and gravel packing, confirming the lab results on filter cake quality. No
matrix stimulation treatments were performed for clean-up and expected gas production rate was
soon exceeded on the well.
LAB TEST AND SIMULATIONS
The first challenge was to design a drill-in fluid that is inhibitive to the shale formations to be drilled
and in the same time protects the reservoir from any damage in order to maximize the production
rates. Fluid Provider customized a solution for the operator which included the Drill in fluid system
optimized with shale stabilizers and encapsulators to mitigate the expected interbedded shale
streaks. The formulation was further improved by customizing sized marble for bridging the
reservoir’s 400md permeability utilizing fluids provider’s proprietary software. Different mixture
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packages were proposed and hence the bridging packages were tested using Particle Plugging
Test (PPT) to validate the optimum Particle Size Distribution (PSD) in lab. The best bridging
material mixture was find to be 40% v/v sized ground marble 50 µ, 50% v/v sized ground marble
25 µ and 10% v/v sized calcium carbonate 5 µ.
Fig 1: Particle Size Distribution
A return permeability study was also required to prove the suitability of the drill-in fluid for the
reservoir section and to ensure that whole fluid is not damaging to the reservoir, minimizing filtrate
invasion. The return permeability study was performed on an artificial core proving 88% regained
permeability.
Tab. 1:
Regain Permeability Test
Second challenge was a complex displacement plan customized for the operation to have the open
hole gravel pack in place. The displacement called for ensuring the open hole is clean of cuttings
and debris then pull inside liner shoe to displace the casing with below wellbore clean-up pill trains
to brine:



50 bbl Push Pill (5% casing cleaner) – push pill for laminar flow and start cleaning action
50 bbl Wash Pill (18% casing cleaner) – main cleaning pill
50 bbl Sweep Pill (5% casing cleaner) – to sweep any debris from cleaning pill out of the
hole
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This ensures displacing the casing to brine while keeping the drill-in fluid in the open hole to avoid
any losses due to the removal of the filter cake. The first stage was to displace the casing
completely to clear brine. The second stage included running in the open hole to bottom and
displace the open hole to brine with a viscous brine spacer ahead at low pump rate to avoid
removal of filter cake. Once the drill-in fluid is 50 meters inside casing, the string was pull up inside
the casing and reverse circulate the drilling fluid out until clean brine returns are observed on
surface. This is to minimize contamination of the whole annulus with the drilling fluid.
The fluid provider used proprietary completion software extensively in the planning phase and
programmed into the plan to ensure adequate annular velocities achieve by the wash pill through
the casing annulus. The simulation was extremely valued and the flow rates at rig site were
followed as per simulation.
JOB EXECUTION SIMULATIONS
The job was pumped at the rate of 4.5 bpm without any trouble using CaCl2 1.13 SG as carrier
fluid and 0.5 ppa 20-40 US-Mesh Carbolite. The increase in rate at the middle of the job in only
due to a technical problem on the pumping unit.
During the job, as a proof of the filter cake quality, no major losses recorded. The job has showed
100% annular packing, as highlighted by the following table. Total infused proppant from surface
was 6,500 lb, which equates to 302 bbls of slurry volume. Final recorded sand out pressure is 5000
psi at 2.3 bpm pumping rate and total reversed out gravel was 3,300 lbs based on the recovered
gravel in the slurry dehydrator. The total gravel passed through X-O port was 3,200 lbs.
Fig 2: Job Log
After the job the upper completion has been run in hole and the volume above the formation
isolation valve was displaced with lighter brine. After opening the valve only few psi of
underbalance were applied in the open hole section. The well was then open to production without
any filter cake removal job or stimulation assuring very good performance without any near well
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bore damage. A relevant saving in operational time and cost has been achieved avoiding this cake
removal job with coiled tubing and having gas at surface already after few minutes.
Tab. 2:
Gravel Requirements
Gravel Requirements
0
lbs
Gravel Amount above Effective SCRN section of Top SCRN due to Sand Out event
157
lbs
Gravel Amount Just due to Slurry Settling above normal BP after Sand Out
19
lbs
Gravel Amount for Packing the Annular Space Till SCRN Section of top SCRN JNT
3,024
lbs
Total Est Gravel
3,200
lbs
Gravel Amount for Perforation Packing
As shown in the following graphs obtained by nodal analysis the production parameters at three
different choke size has been matched with one well performance at zero skin. Already during the
well clean up phases, the production achieved was almost twice the expected target.
Fig 3: IPR evaluation
CONCLUSIONS
By carefully designing the reservoir fluids to effectively sealing the porous formation was mitigated
the potential of causing formation damage.
The customized drill-in fluid has proved to be effective in inhibiting the shale formation while
protecting the reservoir. In addition, the displacement procedure was effective in cleaning the
wellbore from all mud residuals and debris.
No degradation of the filter-cake was experience during the gravel packing execution and
consequently, a gain of 100% annular packing was obtain. This result in term of packing also
means that the selected DIF allows to drill an hole perfectly in gauge.
As highlighted in the nodal analysis results the well is producing with zero skin.
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ACKNOWLEDGEMENTS
This research was supported by Eni and Halliburton. We thank our colleagues from Petrobel who
provided insight and expertise that greatly assisted the research, and for their comments on an
earlier versions of the manuscript.
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