Patent Application
20240079096
The disclosure relates to methods for determining an amount of seawater, an amount of aquifer water, and an amount of original reservoir water in a produced water sample using oxygen isotope ratios and chloride concentrations. An 18O/16O ratio (δ18O) and a chloride concentration are measured for a seawater sample, an aquifer water sample, and an original reservoir water sample and are used to make a mixing model. δ18O and a chloride concentration are measured in a produced water sample and the mixing model can be used to determine the amounts of each constituent in the produced water sample.
Seawater and/or aquifer water can be used for drilling and enhanced oil recovery operations. Reservoirs can contain seawater from power injectors, aquifer water from gravity injections and residual reservoir connate water. Distinguishing between produced waters and in-situ water formation can be difficult due to the injection of aquifer waters and/or seawater. Often, chemical analyses alone (e.g. measurement of Cl concentration) has not been successful in distinguishing water sources.
The disclosure relates to methods for determining an amount of seawater, an amount of aquifer water, and an amount of original reservoir water in a produced water sample using oxygen isotope ratios and chloride concentrations. An 18O/16O ratio (δ18O) and a chloride concentration are measured for a seawater sample, an aquifer water sample, and an original reservoir water sample and are used to make a mixing model. δ18O and a chloride concentration are measured in a produced water sample and the mixing model can be used to determine the amounts of each constituent (seawater, aquifer water and/or original reservoir water) in the produced water sample.
The methods of the disclosure can enable the determination of the source of produced water and the effect of seawater and aquifer water on original in-situ waters. The methods of the disclosure can be used to make operational decisions enabling time and cost savings during drilling and production operations. The methods can be used to identify breakthrough of injection water, monitor water flooding and predict potential scaling problems caused by mixing of incompatible waters.
The methods of the disclosure can be used to analyze a mixture of waters with different salinity (e.g. low salinity aquifer water, moderate salinity seawater and/or high salinity reservoir water) which, in general, cannot be distinguished by chemical analysis. The methods of the disclosure can be compatible with chemical reactions caused by mixing of incompatible waters and chemicals such as scale inhibitors, which may alter the composition of produced water.
The methods of the disclosure employ major cations and anions and the isotope composition of oxygen (18O/16O) in original reservoir water, aquifer water and injected seawater as each water has distinct geochemistry. Oxygen isotopes can be measured with relatively high accuracy and are generally stable over production timescales. Chloride accounts for over 90% of the total anion charge in many water samples and can be accurately measured and the concentration is not readily altered. The methods of the disclosure do not rely on hydrogen isotope ratios (deuterium/hydrogen “D/H”), thereby avoiding any impact on D/H ratios caused by water-rock interactions in deep reservoir water.
In a first aspect, the disclosure provides a method, including measuring an 18O/16O ratio (δ18O) and a chloride concentration for each of a seawater sample, an aquifer water sample, and an original reservoir water sample; measuring δ18O and a chloride concentration in a produced water sample; using the measured δ18O and chloride concentrations for the aquifer water sample, the seawater sample and the original reservoir water sample to make a model; and using the model to determine an amount of seawater, an amount of aquifer water, and an amount of original reservoir water in the produced water sample. The produced water sample includes at least one member selected from the group consisting of the seawater, the aquifer water, and the original reservoir water.
In some embodiments, the model is for a well or formation (t) and is made using the equations
are the amounts of chloride in the seawater, aquifer water and original reservoir water respectively;
VA, VB and VC are the relative volume fractions of the seawater, aquifer water and original reservoir water respectively;
VD is the mixing proportion used in the model;
WH2O—Cl is the mass of water calculated by subtracting chloride per unit volume of liquid in grams per liter; and
δ18O xsewater, δ18O yAquifer water, and δ18O zReservoir water are the oxygen isotope ratios in the seawater, aquifer water and original reservoir water, respectively.
In some embodiments, WH2O—Cl is calculated as
wherein Slope (H2O vs Cl) produced water is the slope from a linear trend line fit to H2O (mg/L) versus Cl (mg/L) for produced water samples.
In some embodiments, an equation to calculate WH2O—Cl is obtained by fitting a linear trend line to chloride concentration values versus
TDS is the total dissolved solids calculated by the sum of all dissolved ions; and
the chloride concentration values, specific gravity and TDS are obtained from the produced water samples.
In some embodiments: the model includes first, second and third endpoints; VA, VB and VC correspond to relative volume percentages of the seawater sample, the aquifer water sample, and the original reservoir water sample, respectively; the first endpoint corresponds to VA=1, VB=0 and VC=0; the second endpoint corresponds to VA=0; VB=1 and VC=0; and the third endpoint corresponds to VA=0, VB=0 and VC=1.
In some embodiments: the model includes first, second and third outer lines that connect the endpoints to define a triangle; the first outer line corresponds to VA being equal to zero while varying VB and VC; the second outer line corresponds to VB being equal to zero while varying VA and VC; and the third outer line corresponds to VC being equal to zero while varying VA and VB.
In some embodiments: the model includes grid lines that connect the outer lines; and each grid lines corresponds to one member selected from the group consisting of VA, VB and VC being at a constant value between 0 and 1 and varying the other two members selected from the group consisting of VA, VB and VC.
In some embodiments: each endpoint corresponds to a mixture including only one member selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample; each outer line corresponds to a mixture including two members selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample; and each grid line corresponds to a mixture including the seawater sample, the aquifer water sample, and the original reservoir water sample.
In some embodiments: a produced water sample including only one member selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample plots close to its corresponding endpoint; a produced water sample including only two of members selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample plots along the outer lines at a position corresponding to an amount of each of the two members; and a produced water sample including the seawater sample, the aquifer water sample, and the original reservoir water sample plots in at a position within the triangle corresponding to an amount of each of the seawater sample, the aquifer water sample, and the original reservoir water sample.
In some embodiments: the model includes endpoints that correspond to mixtures including only one member selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample; the model includes outer lines connecting the endpoints that correspond to mixtures including only two members selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample; the outer lines define a triangle; and the model includes grid lines that connect the outer lines that correspond to mixtures including the seawater sample, the aquifer water sample, and the original reservoir water sample.
In some embodiments: a produced water sample includes only one member selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample plots close to the corresponding endpoint; a produced water sample including two members selected from the group consisting of the seawater sample, the aquifer water sample, and the original reservoir water sample plots along the outer lines at a position corresponding to an amount of each of the two members; and a produced water sample including the seawater sample, the aquifer water sample, and the original reservoir water sample plots at a position within the triangle corresponding to an amount of each of the seawater sample, the aquifer water sample, and the original reservoir water sample.
In some embodiments, the seawater has a concentration of chloride of 5000 mg/L to 40000 mg/L.
In some embodiments, the seawater has a δ18O of −5 to 7.
In some embodiments, the aquifer water has a concentration of chloride of 100 mg/L to 6000 mg/L.
In some embodiments, the aquifer water has a δ18O of −10 to 3.
In some embodiments, the original reservoir water has a concentration of chloride of 40000 mg/L to 250000 mg/L
In some embodiments, the original reservoir water has a δ18O of −2 to 8.
In some embodiments, the produced water is from a production well in fluid communication with an underground reservoir.
In some embodiments, the produced water is from a flowback operation. In some embodiments, the seawater is injected into the underground reservoir
Oxygen isotope ratios can be reported relative to Vienna Standard Mean Ocean Water (VSMOW) using delta notation:
where 18O/16O are atomic abundance ratios.
Mixing proportions of chloride and oxygen isotopes for a well or formation (t) with three mixing components and relative volume percentages VA, VB and VC yield the equations:
wherein: Cl (mg/L) XSewater, Cl (mg/L) yAquifer water, and Cl (mg/L) zReservoir water are the amounts of chloride in the seawater, aquifer water and original reservoir water respectively; VA, VB and VC are the relative volume fractions of the seawater, aquifer water and original reservoir water, respectively; VD is the mixing proportion used in the model; WH2O—Cl is the mass of water calculated by subtracting chloride per unit volume of liquid in grams per liter; and δ18O xSewater, δ18O yAquifer water, and δ18O zReservoir water are the oxygen isotope ratios in the seawater, aquifer water and original reservoir water, respectively. WH2O is unique for each water source (seawater, aquifer water and original reservoir water). Typically, the value of VD is 1.
Conversion of the mass of ions (e.g., chloride) from milligrams per liter of fluid to milligrams per kg of water for use in equation (2) can be performed using the equation:
M(mg/kg water)=M(mg/L)/WH2O—Cl (4)
where M (mg/kg water) and M (mg/L) refer to the mass of chloride in mg/kg water and mg/L, respectively. W is the total amount of water with all dissolved ions. The mass of chloride is divided by the total water (W) to specifically get mg chloride per L of water.
The equations assume ideal mixing but incorporate small corrections for the different concentrations of water in each of the endpoints (seawater, aquifer water and original reservoir water). Endpoint water concentrations can be estimated using the equation:
which is obtained by fitting a linear trend line to chloride concentration values versus
where TDS is the total dissolved solids calculated by the sum of all dissolved ions. Equation (5) is recalculated for each field or well.
The chloride concentrations and oxygen isotope ratios for seawater, aquifer water and original reservoir water should be obtained for a given reservoir. Once obtained, the values can be used to construct the model. Such a model is depicted in
Generally, the model contains three endpoints, where each endpoint corresponds to one of the three components (the seawater, the aquifer water and the original reservoir water). Each endpoint can be determined by setting one of the volume fractions VA, VB and VC, corresponding to the fraction of seawater, aquifer water and original reservoir water respectively, to 1, while setting to other two volume fractions to 0. Specifically, VA=1, VB=0 and VC=0; VA=0; VB=1 and VC=0; and VA=0, VB=0 and VC=1 in equations 2 and 3 provide the three endpoints.
The model additionally contains outer lines connecting the endpoints that correspond to mixtures of two of the components. The outer lines can be obtained by setting one of VA, VB and VC to 0 and varying the other two parameters. The model can further contain grid lines that connect the outer lines that correspond to mixtures of the three components. The grid lines can be obtained by holding one of VA, VB and VC at a constant value between 0 and 1 and not equal to 0 or 1 and varying the other two components.
Generally, a produced water sample containing only one of the components will plot close to the corresponding endpoint. A produced water sample containing only two of the components will plot along the outer lines at a position corresponding to an amount of each of the two components. A produced water sample containing all three of the components will plot in the center of the triangle at a position corresponding to an amount of each of the three components.
In general, chloride concentrations can be measured using any appropriate technique. As an example, in some embodiments, chloride concentrations are measured by potentiometric titration, such as, for example, potentiometric titration performed with silver nitrate.
Generally, cations and/or anions can be measures using any appropriate technique. As an example, in some embodiments, cations and/or anions are measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).
Typically, isotope concentrations in a water sample can be measured using any appropriate technique. As an example, in certain embodiments, the amount of 16O and/or 18O is measured using a wavelength-scanned cavity ring-down spectroscopy (WS-CRDS). As another example, in certain embodiments, the amount of 16O and/or 18O can be measured using mass spectrometry.
In certain embodiments, the concentration of chloride in the seawater, the aquifer water and/or the original reservoir water depends on the geographical location of the water. In some embodiments, the seawater has a concentration of chloride of at least 5000 (e.g., at least 10000, at least 15000, at least 20000, at least 25000, at least 30000, at least 35000) mg/L and at most 40000 (e.g., at most 35000, at most 30000, at most 25000, at most 20000, at most 15000, at most 10000) mg/L. In some embodiments, the aquifer water has a concentration of chloride of at least 100 (e.g., at least 500, at least 1000, at least 1500, at least 2000, at least 2500, at least 3000, at least 3500, at least 4000, at least 4500, at least 5000, at least 5500) mg/L and at most 6000 (e.g., at most 5500, at most 5000, at most 4500, at most 4000, at most 3500, at most 3000, at most 2500, at most 2000, at most 1500, at most 1000, at most 500) mg/L. In some embodiments, the original reservoir water has a concentration of chloride of at least 40000 (e.g., at least 50000, at least 100000, at least 150000, at least 200000) mg/L and at most 250000 mg/L (e.g., at most 200000, at most 150000, at least 100000, at least 50000) mg/L.
In certain embodiments, the δ18O of the seawater, the aquifer water and/or the original reservoir water depends on the geographical location of the water. In certain embodiments, the seawater has a δ18O of at least −5 (e.g., at least −4, at least −3, at least −2, at least −1, at least 0, at least 1, at least 2, at least 3, at least 4, at least 5) and at most 7 (e.g., at most 6, at most 5, at most 4, at most 3, at most 2, at most 1, at most 0, at most −1, at most −2, at most −3). In certain embodiments, the aquifer water has a δ18O of at least −10 (e.g., at least −9, at least −8, at least −7, at least −6, at least −5) and at most −3 (e.g., at most −4, at most −5, at most −6, at most −7, at most −8). In certain embodiments, the original reservoir water has a δ18O of at least −2 (e.g., at least −1, at least 0, at least 1, at least 2, at least 3, at least 4, at least 5, at least 6) and at most 8 (e.g., at most 7, at most 6, at most 5, at most 4, at most 3, at most 2, at most 1, at most 0).
Example 1—Construction of Mixing Model
Chloride and cation concentrations and δ18O were measured for samples of seawater, aquifer water and original reservoir water. Cation concentrations for produced water samples were measured by ICP-AES (7850 ICP-MS, Agilent Technologies and ICP-OES spectrometer 240FS AA, Agilent Technologies) for use in equation (6).
Chloride concentrations were determined by potentiometric titration with silver nitrate solution with a glass silver/silver chloride electrode. During titration an electronic voltmeter (Mettler DL-77 Auto Titrator) was used to detect the change in potential between the two electrodes. The end point of the titration was detected by the instrument. Quality control check standard were run with the samples to ensure accuracy of results. The measurements were generally accurate to ±3% and were rejected if they differed by more than ±5% from the expected values.
The chloride concentrations for samples of seawater, aquifer water and original reservoir water were used to calculate WH2O—Cl using equation (5).
δ18O were measured using both wavelength-scanned cavity ring-down spectroscopy mass spectrometry.
δ18O of the samples were measured using a Picarro L2130-i Laser Cavity Ring-Down Spectroscopy (CRDS) instrument. 5 μl of sample was injected into a vaporizer a total of 8 times. The temperature and pressure were kept constant at 110° C. and 3.5 psig inside the line to ensure total and instantaneous vaporization of the water without isotopic fractionation.
For mass spectrometry measurements, 5 ml aliquots of sample were placed in 25 ml glass vials, attached to a vacuum manifold and immersed in a water bath regulated to 18.0±0.2° C. The manifold was used to remove air and add 0.7-0.9 bars of carbon dioxide. Isotopic equilibration between carbon dioxide and water was achieved overnight. The equilibrated gases were passed over acetone slush (−90-−96° C.) to remove water vapor. The gases were then introduced into a dual-inlet Finnigan-MAT Delta S stable isotope ratio mass spectrometer using automated valves. Water standards (USGS-48, USGS-47, USGS-48, USGS-50, PRIMARY VSMOW STANDARD, and three other lab made standards) were used to calibrate the isotope ratios and report them relative to standard mean ocean water (SMOW) using delta notation.
Reproducibilities, estimated by pooling standard deviations for replicate analyses of standards were ±0.13% for δ18O for both instruments.
The oxygen isotope ratios, chloride concentrations and calculated total water for the seawater, aquifer and original reservoir water samples measured are presented in table 1.
The values of VA, VB and VC were each set to 1 while the other two were set to 0 in equations 2 and 3 to provide the values for the endpoints of the model, as shown in table 2.
The outer lines and grid lines of the model were calculated by varying the values of VA, VB and VC in equations 2 and 3. Tables 3 and 4 shows the values of δ18O and Chloride concentration used to make the outer lines and the grid lines, respectively.
The mixing model is shown in
Example 2—Characterization of Produced Water Samples
The mixing model generated in Example 1 was used to determine the composition of produced water samples. Chloride concentrations and δ18O of 128 produced water samples from five different wells in the same field and reservoir taken during different field operations were determined using the methods described in Example 1.
Produced water samples “A” plot very closed to the aquifer water end-member, suggesting that the produced water was composed almost entirely of injected aquifer water. However, a few samples plot along the line between the aquifer water and original reservoir water, which suggests mixing between the original reservoir and aquifer water sources.
Produced water samples “B” were nearly 60% original reservoir water, 20% injected seater and 20% aquifer water.
Produced water samples “BB” contained all three water sources and were divided into two clusters. Some of the “BB” samples contained mainly of injected seawater (over 70%). The other samples were distributed between the three sources. This indicates that seawater and aquifer water were injected into the original reservoir water, causing the produced water samples to possess all three water sources.
Produced water sample “C” plot along the aquifer water and original reservoir water line. Thus, this sample was composed of a mixture of aquifer water and original reservoir water with minimal effect of seawater.
Produced water sample “D” plot along the mixing line between injected seawater and original reservoir water, suggesting that most of the samples was composed of injected seawater with small amounts of original reservoir water and fresh aquifer water.
The mixing model was successfully applied to produced water to help predict and estimate the source of produced water and the effect of seawater and/or aquifer water on the original reservoir water. This information can help make quick field operation decisions, thereby saving time and reducing costs in drilling and production operations.
