SECTION A9 PETROPHYSICAL PROPERTIES

Transcription

1 FORMATE TECHNICAL MANUAL C A B O T CHEMICAL AND PHYSICAL PROPERTIES SECTION A9 PETROPHYSICAL PROPERTIES A9.1 Introduction...2 A9.2 Resistivity...2 A9.2.1 Introduction...2 A9.2.2 Resistivity in single-salt formate brines...2 A9.2.3 Resistivity in blended formate brines...2 A9.2.4 Resistivity temperature dependence...2 A A9.4 Sonic velocity...11 References...11 The Formate Technical Manual is continually updated. To check if a newer version of this section exists please visit formatebrines.com/manual NOTICE AND DISCLAIMER. The data and conclusions contained herein are based on work believed to be reliable; however, CABOT cannot and does not guarantee that similar results and/or conclusions will be obtained by others. This information is provided as a convenience and for informational purposes only. No guarantee or warranty as to this information, or any product to which it relates, is given or implied. CABOT DISCLAIMS ALL WARRANTIES EXPRESS OR IMPLIED, INCLUDING MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE AS TO (i) SUCH INFORMATION, (ii) ANY PRODUCT OR (iii) INTELLECTUAL PROPERTY INFRINGEMENT. In no event is CABOT responsible for, and CABOT does not accept and hereby disclaims liability for, any damages whatsoever in connection with the use of or reliance on this information or any product to which it relates Cabot Corporation, MA, USA. All rights reserved. CABOT is a registered trademark of Cabot Corporation.

2 CABOT FORMATE TECHNICAL MANUAL A9.1 Introduction Logging in formate brines has been considered a challenge to well-log interpretation because both formate-based drilling fluids and formate brine filtrates have properties that are significantly different from conventional oil- and water-based muds [1][2][3]. These include resistivity, nuclear properties, and density. A9.2 Resistivity A9.2.1 Introduction Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge. The SI unit of electrical resistivity is the ohm meter. The electrical resistivity ρ(rho) of a material is usually defined by the following: ρ = RA I Where ρ = static resistivity (ohm m) R = electrical resistance of the specimen (ohm) I = length of the specimen (m) A = cross-sectional area of the specimen (m 2 ) The electrical resistivity of drilling and completion fluids is an important parameter for the loggers. Formate brines contain high amounts of salts, and therefore have very high conductivity and low resistivity. (1) A9.2.3 Resistivity in blended formate brines Blended potassium and cesium formate brines are normally composed of two saturated brines (standard blend) or a saturated cesium formate brine and a slightly diluted potassium formate brine (diluted blend, sometimes used in winter). Resistivity measurements by Westport Technology Center International, Houston and Cabot Operations and Technical Support Laboratory, Aberdeen, UK [4] have shown that resistivity is a linear function of fluid density in a mixed blend of potassium and cesium formate. The predicted resistivity at 15.6 C / 60 F for a standard blend and a diluted blend are shown in Figure 2. Resistivities are therefore easy to predict for blended brines by drawing a straight line between the densities of the pure brines that are blended. Similar predictions can be made for potassium / sodium formate blends and sodium / cesium formate blends. A9.2.4 Resistivity temperature dependence In formate brines, as in other aqueous salt solutions, resistivity decreases with increased temperature. The resistivity of blended potassium and cesium formate (1.92 g/cm 3 / 16.0 lb/gal standard blend) has been measured as a function of dilution and temperature. Results are plotted in Figure 3. As can be seen, temperature has a greater effect on resistivity the more diluted the fluid is. The effect of temperature on resistivity is also greater at lower, rather than higher temperatures. A9.2.2 Resistivity in single-salt formate brines Resistivity values for sodium formate, potassium formate, and cesium formate single-salt brines as a function of salt concentration at 15.6 C / 60 F are shown in Figure 1 and Table 1. All data is based on measurements made by Westport Technology Center International, Houston and Cabot Operations and Technical Support Laboratory, Aberdeen, UK [4]. It is interesting to note how resistivity in single-salt formate brines is lowest at medium concentration. At the high end of the concentration scale (as well as the low), resistivity is significantly higher. PAGE 2 SECTION A9

3 SECTION A: CHEMICAL AND PHYSICAL PROPERTIES CABOT METRIC Resistivity at 15.6 C 0.30 Resistivity [ohm-m] Resistivity [ohm-m] FIELD [g/cm 3 ] Resistivity at 60 F NaFo KFo CsFo NaFo KFo CsFo [lb/gal] Figure 1 Resistivity of sodium, potassium, and cesium formate single-salt brines as a function of formate concentration at standard conditions (15.6 C / 60 F). SECTION A9 PAGE 3

4 CABOT FORMATE TECHNICAL MANUAL Table 1 Resistivity of sodium, potassium, and cesium formate single-salt brines at standard conditions (15.6 C / 60 F). METRIC Resistivity [ohm m] Resistivity [ohm m] [g/cm 3 ] NaFo KFo CsFo [lb/gal] NaFo KFo CsFo FIELD PAGE 4 SECTION A9

5 SECTION A: CHEMICAL AND PHYSICAL PROPERTIES CABOT METRIC Resistivity in potassium / cesium formate blends at 15.6 C g/cm 3 KFo KFo CsFo Resistivity [ohm-m] g/cm 3 KFo CsKFo standard blend (CsFo 2.2 g/cm 3, KFo 1.57 g/cm 3 ) CsKFo diluted blend (CsFo 2.2 g/cm 3, KFo 1.54 g/cm 3 ) 2.2 g/cm 3 CsFo [g/cm 3 ] FIELD Resistivity in potassium / cesium formate blends at 60 F lb/gal KFo KFo CsFo CsKFo standard blend (CsFo 18.3 lb/gal KFo 13.1 lb/gal) CsKFo diluted blend (CsFo 18.3 lb/gal KFo 12.8 lb/gal) Resistivity [ohm-m] lb/gal KFo 18.3 lb/gal CsFo [lb/gal] Figure 2 Resistivity as a function of brine density for two different potassium and cesium formate blends. The one blend is a standard blend based on 1.57 g/cm 3 / 13.1 lb/gal potassium formate brine and 2.20 g/cm 3 / 18.3 lb/gal cesium formate brine. The other blend is a diluted blend (1.54 g/cm 3 / 12.8 lb/gal potassium formate and 2.20 g/cm 3 / 18.3 lb/gal cesium formate) that is often used in the winter. SECTION A9 PAGE 5

6 CABOT FORMATE TECHNICAL MANUAL Resistivity [ohm-m] Resistivity vs. temperature Temperature [ F] %wt %wt %wt %wt %wt %wt %wt Temperature [ C] Figure 3 Resistivity as a function of temperature for various dilutions of 1.92 g/cm 3 / 16.0 lb/gal potassium / cesium formate brine. A9.3 (HI) is an important property in the response of a neutron porosity log. The of a material is defined as the number of hydrogen atoms per unit volume divided by the number of hydrogen atoms per unit volume of pure water at 75 F. for a brine of a given concentration (density) can be calculated when the exact composition of the brine is known. as a function of brine density for single-salt sodium, potassium, and cesium formate brines are given in Table 2 (metric) and Table 3 (field). These values are calculated from the composition data given in Section A2, Brine and PVT Data. for potassium and cesium formate brine blends can be calculated easily from the of the two brines that are blended according to the following linear relationship: HI CsKFo = HI KFo x Where HI CsKFo HI CsFo HI KFo σ CsKFo σ CsFo σ KFo (HI CsKFo HI KFo ) (σ CsKFo σ KFo ) (σ CsFo σ KFo ) = HI for blended brine = HI for stock CsFo brine = HI for stock KFo brine = or g/cm 3 of blended brine = or g/cm 3 of stock CsFo brine = or g/cm 3 of stock KFo brine The equation is valid for all density units, but they need to be consistent. The for the two most commonly used cesium potassium formate brine blends are listed in Table 4 to Table 5 for metric and field units. PAGE 6 SECTION A9

7 SECTION A: CHEMICAL AND PHYSICAL PROPERTIES CABOT Table 2 for sodium, potassium, and cesium formate single-salt brines as a function of brine density. METRIC METRIC METRIC Sodium formate Potassium formate Cesium formate [g/cm 3 ] %wt NaFo [g/cm 3 ] %wt KFo [g/cm 3 ] %wt CsFo SECTION 2.34 A9 84.5PAGE

8 CABOT FORMATE TECHNICAL MANUAL Table 3 for sodium, potassium, and cesium formate single-salt brines as a function of brine density. FIELD FIELD FIELD Sodium formate Potassium formate Cesium formate [lb/gal] %wt NaFo [lb/gal] %wt KFo [lb/gal] %wt CsFo PAGE 8 SECTION A9

9 SECTION A: CHEMICAL AND PHYSICAL PROPERTIES CABOT Table 4 for standard potassium / cesium formate blends composed of 1.57 g/cm 3 potassium formate and 2.20 g/cm 3 cesium formate. METRIC [g/cm 3 ] %wt KFo %wt CsFo %wt H VERSION / SECTION 20.1 A9 PAGE

10 CABOT FORMATE TECHNICAL MANUAL Table 5 for standard potassium / cesium formate blends composed of lb/gal potassium formate and lb/gal cesium formate. FIELD [lb/gal] %wt KFo %wt CsFo %wt H PAGE 10 SECTION A9

11 SECTION A: CHEMICAL AND PHYSICAL PROPERTIES CABOT A9.4 Sonic velocity Sonic velocity is an important property for logging. There is very little sonic data available on formate brines in the open literature. Available sonic velocity data for some formate brines are listed in Table 6. The data is taken from various sources and might not be accurate. Table 6 Sonic velocity for three typical formate compositions. Brine type Temperature Pressure Sonic velocity g/cm 3 lb/gal C F Pa [psi] [m/s] [ft/s] Composition NaFo ,880 6,168 KFo ,960 6,430 KFo ,951 6,402 76% KFo CsKFo ,895 6, % Cs / 85.63% K, / ml, / g CsFo ,550 5,085 CsFo ,580 5,185 83% CsFo References [1] Pedersen, B.K.: Understanding the Effects of Cesium / Potassium Formate Fluid on Well Log Response A Case Study on the Kristin and Kvitebjørn Fields, Offshore Norway, SPE , September [2] Galford, J. et al: Borehole and Formation Invasion Effects of Formate-Based Mud Systems on Nuclear Logs, SPWLA 46th Annual Logging Symposium, June [3] Pinhjun G., et al: Interpretation of nuclear logs in formate-based drilling fluids in a North Sea well, SPWLA 43rd Annual Logging Symposium, June [4] Resistivity Measurements in Formate Fluids, report # LR-212, Operations and Technical Support Laboratory, Aberdeen, UK, April SECTION A9 PAGE 11