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5ANALYSIS OF SULFATE SALT DEPOSITION IN OIL
PRODUCTION
1Boboev G.G., 2Sheina N.E., 3Mirshamilova M.A
1,2Associated Professor 3Assisstant https://doi.org/10.5281/zenodo.10051308
Abstract. The modern stage of oil production is characterized by the need to extract significant volumes of associated water to the surface, which are pumped back into the reservoir. As a result of watering of extracted products at all stages of development, salt deposition occurs. Sediments, accumulating in the filtration channels of productive formations, on the surface of well equipment, in systems inside the field collection and preparation, lead to significant losses in production and high material costs.
Keywords: oil production, salt deposition, calcium, sulfates, groundwater.
The modern stage of oil production is characterized by the need to extract significant volumes of associated water to the surface, which are pumped back into the reservoir. As a result of watering of extracted products at all stages of development, salt deposition occurs. Sediments, accumulating in the filtration channels of productive formations, on the surface of well equipment, in systems inside the field collection and preparation, lead to significant losses in production and high material costs.
The main reasons for salt deposition are the mixing of incompatible waters during flooding and changes in thermobaric conditions during oil production. Forecasting the process of salt formation during oil production is an integral part of measures to prevent it. Analytical forecasting of salt formation, carried out for specific objects and conditions based on physical and chemical calculations of the composition of produced waters, makes it possible to predict the possibility of salt precipitation along the entire path of the oil production process.
Groundwater is a complex physical and chemical system that is in close relationship and equilibrium with other phases of the earth's crust. One of the physicochemical equilibriums is sulfate-calcium, which characterizes the balance between the contents of calcium and sulfates in groundwater.
There are three main types of sulfate-calcium equilibrium in groundwater:
1. when the content of calcium ions and sulfate ions is approximately equal;
2. when sulfate ion predominates over calcium ion in waters;
3. when the content of calcium ions is greater than sulfate ion.
The first type of sulfate-calcium equilibrium is characteristic of the process of leaching of gypsum and anhydrites, which includes impermeable waters C1s(tr+st), they are enriched with sulfate ion. The second type of sulfate-calcium equilibrium is characterized mainly by mineralized groundwater, found in zones of significant water exchange. The third type of sulfate-calcium equilibrium is observed in highly mineralized waters in zones of slow and extremely slow water exchange.
Reservoir waters of oil fields in the northern part of the Trade and Production Enterprise (TPE) belong mainly to the third type of sulfate-calcium equilibrium, i.e. highly mineralized
waters of zones of slow and extremely slow water exchange, impermeable waters Cis(tr+st) belong to the first type and are a source of sulfate ion.
Predicting the process of salt formation during oil production makes it possible to determine the critical parameters at which salt deposition begins. There are many methods for predicting the formation of sulfate salts. Each method has its own area of application; in this work, methods are used that are based on experimental data on the solubility product.
The degree of saturation of formation waters in the northern part of the TPP with calcium sulfate (CaSO4), strontium sulfate (SrSO4), was calculated using the Chistovsky method and is shown in Table i.
Table 1 - Degree of saturation of formation waters with calcium and strontium sulfates
according to the Chistovsky method
Field Saturation degree Saturation degree
CaSO4 SrSO4
Ardalinskoe 0,8624 1,1116
East Kolvinskoe 1,3118 2,0317
Dyusushevskoe 1,7213 1,9901
Oshkotynskoe 1,2503 1,4204
It should be noted that the waters of the East Kolvinskoye, Dyusushevskoye, and Oshkotyn deposits are highly saturated with calcium sulfate, and the waters of these deposits and the Ardalinskoye deposit with strontium sulfate.
Index of formation water saturation with calcium and strontium sulfates, calculated using the method of J.E.Oddo and M.B.Thomson, is given in tables 2, 3.
Table 2 - Saturation index of formation waters with calcium sulfate according to the Oddo
method and Thomson
Field Temperatu Pressure, Saturation Saturation Saturation index
re MPa index index (bessanite)
oc (gypsum) (anhydrite)
Dyusushevskoe 82 34 0,5566 0,5424 0,821405
East Kolvinskoe 87 37 0,0724 0,1430 0,38607
78 33 0,7176 0,8069 1,068622
81 34 0,4372 0,4707 0,735868
75 32 0,1216 0,0145 0,34208
Based on calculations, it can be noted that formation waters of oil fields have a high degree of saturation with calcium sulfate. Among the calcium sulfate salts, the maximum saturation index with bessanite and high saturation with gypsum and anhydrite of the formation waters of the Dyusushevskoye and Vostochno-Kolvinskoye fields are noted, and the Oshkotynskoye field - only with gypsum and bessanite.
The maximum index of formation water saturation with strontium sulfate is observed in the waters of the Upper Devonian sediments of the Dyusushevskoye field, high saturation is observed in the waters of the East Kolvinskoye and Oshkotynskoye fields.
The studies carried out show that according to both methods, the formation waters of the Ardalinsky group of fields are saturated with calcium and strontium sulfates.
Table 3 - Index of water saturation with strontium sulfate according to the Oddo and
Thomson method
Field Age Temperature oc Pressure Mna Saturation index (^.necTHH)
Dyusushevskoe D3 f3 +fm 78 32 0,2432
D3 f3 +fm 77 32 0,3966
D3 f3 +fm 83 34 0,3878
D3 f3 +fm 76 31 0,3001
D3 f2 (dm)+f3 88 37 0,3415
D3 f2 (dm)+ f3 75 32 0,2361
C 1s(tr+st) 65 29 0,1327
Oshkotynskoe East Kolvinskoe C3 65 29 0,2458
D3 f3 +fm1 87 36 0,3458
D3 f3 +fm1 88 37 0,0056
D3 f3 +fm1 90 38 0,1913
D3 f3 +fm1 89 38 0,1188
D3 £2+3 +fm1 78 33 0,1099
The results of determining the structure of the pore space and the distribution of pores along the radius were carried out on the sediment core of the productive horizons of the Upper Devonian of the Ardalinsky group of fields (Polar Lights Company LLC), which are represented by dense and organogenic-detrital limestones, dolomites. Porous, porous-fractured, porous-cavern type reservoirs with a sharp anisotropy of filtration properties are installed here.
Based on the analysis of laboratory core studies, it was established that for the reservoirs of the Vostochno-Kolvinskoye and Dyusushevskoye fields, pore radii of up to 0.12 p,m are most characteristic, and for the Oshkotynsky field, several intervals of pore radii are noted (up to 0.145; 1.45-14.5; more than 29 ^m).
Calculations of the parameters of in-situ deposition of calcium and strontium sulfates were performed (Tables 4, 5).
Based on the values of the pore radii from which sedimentation begins in the formation when crossing the line of average values, the boundary values of the proportion of pores in which deposition of calcium sulfate (Figure 1) and strontium sulfate (Figure 2) are possible are identified. Similar graphs were constructed for all fields of the Ardalin group.
The deposition of calcium sulfate in the productive formations of the East Kolvinskoye and Dyusushevskoye fields should be expected up to 50% of the pores, and in the Oshkotynskoye field - up to 77% at low values of surface tension (Figure 1, Table 6).
The conducted studies show that in the productive formations of the fields under consideration there is a significant probability of changes in the filtration characteristics of the reservoir due to the deposition of calcium and strontium sulfates.
Table 3 - Parameters of calcium sulfate deposition in the pore space productive formations
Field Saturation Surface The radius of Quantity Portion of
index tension, the pores salts in the pores
h/m from which pores, in which it is
C/Co it begins salt deposition, MKM fg depositedCa SO4, %
Oshkotynsk 1,250251 0,012 0,189 0,0002 77
oe 0,370 5,820 6,40 32
1,050 16,500 145,85 22
Dyusushev 1,721257 0,012 0,053 1,54 50
skoe 0,370 1,630 0,45 38
1,050 4,620 10,18 28
3,73742 0,012 0,015 1,072 50
0,370 0,452 0,.031 42
1,050 1,290 0,724 40
East 1,311764 0,012 0,148 0,0001 49
Kolvinskoe 0,370 0,456 0,004 48
1,050 1,300 0,083 37
3,186525 0,012 0,018 0,000002 50
0,370 0,566 0,046 48
1,050 0,750 0,106 47
6,249529 0,012 0,009 0,0000004 50
0,370 0,290 0,012 49
1,050 0,375 0,027 48
paguyc nop, mkm
• 1 - 23 A CP.3H.
Figure 1 - Distribution of pores along the radius in the East Kolvinsky reservoir
Place of Birth
Thus, when pumping produced water into the productive formation of the Ardalin field, one should expect the deposition of calcium sulfate in 75% of the pores at low values of surface tension, and at high values - up to 50% of the pores.
Strontium sulfate deposition when pumping produced water into the formation should be expected in up to 75% of the pores.
The above studies show that when producing produced water is pumped, calcium and strontium sulfates are deposited in the productive formation of the Ardalin field.
Conducted studies indicate that with each subsequent treatment, the hydrochloric acid solution affects new layers, and the filtration channels are gradually filled with deposits of sulfate salts.
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