Acid dissolving power
How much calcite or dolomite a cubic metre of acid dissolves: the gravimetric (β) and volumetric (X) dissolving power from the reaction stoichiometry, the mass of rock dissolved and the CO₂ released.
β₁₀₀ = ν_m · M_m / (ν_a · M_a)β = C · β₁₀₀X = β · ρ_a / ρ_mStoichiometry: 2 moles of a monoprotic acid per mole of calcite, 4 per mole of dolomite, the reaction going to completion. Formic and acetic acids are weak: at reservoir CO₂ pressure the reaction stops at equilibrium, and the real dissolving power is lower. Mineral densities: calcite 2 710, dolomite 2 870 kg/m³. The CO₂ volume is at standard conditions; in the reservoir most of it dissolves in the spent acid.
Source: Economides, Hill, Ehlig-Economides, Petroleum Production Systems (1994): acid dissolving power table; Schechter, Oil Well Stimulation (1992)
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Usually 10–15 % for sandstones, up to 24–28 % in carbonates.
HCl at 20 °C: 10 % — 1 047, 15 % — 1 073, 20 % — 1 098, 28 % — 1 139 kg/m³.
Unit converter for this formulaDensity and °API · Gas-oil ratio · Fraction and percent
- kg/m³850
- g/cm³0.85
- t/m³0.85
- rel. (water 4 °C)0.850024
- lb/ft³53.0638
- lb/gal (ppg)7.09359
- SG (60/60 °F)0.850837
- °API34.8068
°API and SG refer to the density at 60 °F (15.6 °C) relative to water at 60 °F, relative density to water at 4 °C. The oil's thermal expansion between the measurement temperatures is not included. °API = 141.5 / SG − 131.5.
- β — Gravimetric dissolving power–kg rock / kg solution
- m — Rock dissolved by 1 m³ of acid–kg/m³
- V_CO₂ — CO₂ released per m³ of acid (standard conditions)–
More in Fracturing and acidizing
Formation fracture pressure by Eaton's method: the minimum horizontal stress from the overburden and pore pressures through Poisson's ratio. The gradient is given in kPa/m or as an equivalent density.
Expected surface pressure while pumping: the bottomhole treating pressure minus the hydrostatic head plus the friction in the pipe and through the perforations, and the hydraulic power of the pump fleet.
Pressure drop across the perforations: for limited-entry fracturing and for estimating the number of open perforations from a step-down test.
Proppant mass and slurry volume and density for a frac stage from the clean fluid volume and the proppant concentration in kilograms per cubic metre of fluid (in ppa, pounds added per gallon).
Dimensionless fracture conductivity F_CD, the equivalent skin and effective wellbore radius after fracturing from the Cinco-Ley and Samaniego chart, and the fold increase in productivity in pseudo-steady-state flow.
Volume of acid to fill the pores and dissolve the carbonate minerals in a ring around the well out to a given radius: in total and per metre of pay. The typical case is the hydrochloric acid preflush ahead of a mud acid treatment of a sandstone.
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.