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9TECHNICAL SCIENCES
OPENING OF A PRODUCTIVE RESERVOIR DURING DRILLING
Muslim A.
Master of Oil and Gas Faculty 6M07202 - Petroleum Engineering Atyrau University of Oil and Gas named after Saf Utebayev
DOI: 10.5281/zenodo.7607431
Abstract
When opening a formation during drilling, it is important to prevent the penetration of drilling fluid into the formation. The quality of the formation opening, along with high-quality cementing of the production column, repair and insulation work, well development, completion are factors affecting oil recovery and oil recovery coefficient (ORC), allowing to obtain correct data on the oil and gas content of individual productive deposits, the effective thickness of the formation.
Technologies for opening and testing promising subsurface areas should allow preserving the natural state of the reservoir in order to obtain reliable results of testing for industrial oil and gas inflow.
Keywords: drilling, deposit, productive formation, cementing, column centering.
Introduction. To ensure the rapid and high-quality development of the well, it is necessary to prevent the penetration of drilling mud into the formation during drilling, since at the same time weighting agents (barite, hematite, clay particles, etc.) fall out of it.
The experience of using water-based drilling fluids proves that the penetration of filtrate and drilling mud into the formation during autopsies are the main reason for the decrease in the natural properties of the collector.
Water penetrating into the formation reduces its permeability by 50% or more.
This complicates the cementing process and introduces inaccuracy in the estimated height of the cement mortar behind the column.
The density of the drilling mud should provide the necessary back pressure on the formation, preventing emissions, open gushing and other complications.
Productive layers must be opened taking into account the following factors:
physical and geological properties of the reservoir; physico-chemical characteristics of the fluids saturating it;
the correct use of clay solutions, which often worsen the filtration characteristics of the reservoir, especially in low-permeability reservoirs;
the correct application at great depths of weighted drilling fluids with a density of 2200 kg / m3, when drilling mud filtrate and weighting particles penetrate into the productive formation, which irreversibly reduce the permeability of the formation in the bottom-hole zone and lead to uncontrolled hydraulic fracturing (FRACKING) with the penetration of a large amount of liquid and solid phase;
pressure drops of 10 MPa and above should not be allowed, especially at great depths;
when the pressure in the reservoir is below the hydrostatic, it is unacceptable to use clay solutions;
it is correct to open the reservoir in 2 stages: drilling to the roof of the productive reservoir, then opening the productive reservoir, cementing the production column, perforation and development of [1,2]. Descent of the production column.
After opening the productive reservoir and carrying out logging operations, an operational column, strictly centered, is lowered into the well.
For this purpose, special rubber rings, spring lights and other devices are used.
Strict centering of the column ensures uniform distribution of the cement mortar, eliminates the breakthrough of foreign waters into the productive reservoir, backwater circulation of water and gas, etc.
Various designs of wells are used - 1-, 2- and 3-column wells, with the descent of a pre-perforated shank, with the use of various downhole filters and structures with open faces that are not fixed within the productive reservoir by casing columns [3,4].
Layers expressed by dense rocks (limestone, sandstone) are usually not blocked by a column, but are exploited by wells with an open face.
In this case, the casing shoe is cemented in front of the roof of the productive formation.
Then the formation is opened with a chisel of a smaller diameter, and the borehole against the productive formation is left open.
The well is drilled to the bottom of the formation, and the casing is lowered into it.
Then, above the roof of the formation, the column is cemented according to the method of cuff filling.
The space between the lower part of the column and the exposed surface of the formation remains open. The advantage of an open face is its hydrodynamic perfection.
Fountain fittings or faceplate with suspended pumping pipes are installed on the column head.
There are 1 -, 2 -, 3 -, 4 - and 5-column heads designed for working pressure equal to 14, 21, 35, 50 and 70 MPa.
In some cases (on gas wells), column heads designed for pressure up to 150 MPa [5] are used.
An example is given of determining the values of Ka, Kp, p0 for the intervals of the well depths of the Kopa deposit.
I- interval 0-70 m.
z=70 m PmL=0.70 MPa
We determine the coefficient of anomaly Ka=0.7 106/1000 10 70=1 Calculate the hydraulic fracturing pressure from the following expression:
Pr.p.=0.0083-z+0.66-PnJ,., MPa Pr.p =0.0083-70+0.66-0.7=1.04 MPa. The absorption pressure is determined by the following formula:
Pn=0.85Pr.p., MPa Pn=0.85 1.04=0.88 MPa.
We determine the absorption coefficient from the expression
Kn=0.88 106/1000 10 70=1.25 The density of the drilling mud is determined by the formula
P0=1(1.1-1.15)=1.1^1.15 kg/m3
II- interval 70-540 m. z=540 m Pnn=5.4 MPa Ka=5.4106/ 1000 10540=1 Pr.p=0.0083 540+0.66 5.4=8.04 MPa Pn=0.858.04=6.83 MPa
Kn=6.83 106/ 1000 10 540=1.26 po=1(1.1-1.15)=1.1^1.15 kg/m3
III- interval 540-750 m. z=750 m Pnn=7.5 MPa Ka=7.5 106/ 1000 10 750=1
Pr.p =0.0083 750+0.66 7.5=11.17 MPa Pn=0.85 11.75=9.49 MPa Kn=9.49 106/ 1000 10 750=1.26 po=1(1.1-1.15)=1.1^1.15 kg/m3
IV- interval 750-940 m. z=940 m Pnn=9.7 MPa Ka=9.7 106/ 1000 10 970=1.03 Pr.p=0.0083 940+0.66 9.7=14.2 MPa Pn=0.85 14.2=12.07 MPa Kn=12.7 106/ 1000 10 940=1.28 po=1.03(1.1^1.15)=1.13^1.18 kg/m3
V- interval 940-1200 m. z=1200 m Pnn=12.6 MPa Ka=12.6106/ 1000 10 1200=1.05
Pr.p =0.0083 • 1200+0.66 12.6=18.34 MPa Pn=0.85 18.34=15.58 MPa Kn=15.58 106/ 1000 10 1200=1.29 P0=1.05(1.1^1.15)=1.15^1.2 kg/m3
VI- interval 1200-1400 m. z=1400 m Pnn.=14.7 MPa Ka=14.7 106/ 1000 10 1400=1.05 Pr.p=0.0083 1400+0.66 14.7=21.32 MPa Pn=0.8521.32=18.12 MPa
Kn=18.2 106/ 1000 10 1400=1.3 P0=1.05 (1.05^1.1)=1.1^1.15 kg/m3
VII- interval 1400-1450 m. z=1450 m Pn„=15.37 MPa Ka=15.37 106/ 1000 10 1450=1.06
Pr.p =0.0083 • 1450+0.66 15.37=22.17 MPa Pn=0.85 22.17=18.84 MPa Kn=18.84 106/ 1000 10 1450=1.3 P0=1.06 (1.05^1.1)=1.11^1.15 kg/m3
VIII- interval 1450-1600 m. z=1600 m P™=17.12 MPa Ka=17.12 106/ 1000 10 1600=1.07
Рг.р =0.0083 • 1600+0.66 17.12=24.57 MPa Рп=0.85 24.57=20.88 MPa Кп=20.88 106/ 1000 101600=1.3 po=1.07 (1.05^1.1)=1.12^1.17 kg/m3
IX- interval 1600-1750 m. z=1750 м Рпл =18.72 MPa Ка=18.72 106/ 1000 10 1750=1.06
Рг.р =0.0083 • 1750+0.66 18.72=26.88 MPa Рп=0.85 26.88=22.84 MPa Кп=22.84 106/ 1000 10 1750=1.3 po=1.06 (1.05^1.1)=1.11^1.15 kg/m3
X- interval 1750-1800 m. z=1800 м Рпл =19.44 MPa Ка=19.44 106/ 1000 10 1800=1.08
Рг.р =0.0083 1800+0.66 19.44=27.77 MPa Рп=0.8527.77=23.60 MPa Кп=23.60 106/ 1000 10 1800=1.31 po=1.08 (1.05^1.1)=1.13^1.18 kg/m3
Conclusions. If the productive formation is expressed by loose weakly cemented rocks (sands), then the bottom of the well is equipped with a filter. The casing shoe is lowered to the roof of the formation and cemented.
Then a filter shank with small round or slit-shaped holes is lowered into the well, the upper end of which is fixed in the shoe of the casing with oil seals.
The most common wells with a perforated face. In this case, the trunk is drilled to the design depth. Before the casing is lowered, the trunk is examined by geophysical methods to establish oil, water and gas saturated intervals.
After that, the production column is lowered, which is cemented from the face to the required height, and then perforated at the scheduled intervals.
After the casing is lowered, the wellhead is equipped with a special column head designed for strapping the lowered casing columns and sealing the inter-tube space.
References
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