The technical world of formates
Our Formate Technical Manual is by far the most comprehensive work on formate brines ever published. It contains information on cesium, potassium and sodium formate brines collated from 30 years of research and field experience. Split into three sections: chemical and physical properties, compatibilities and interactions, and formate field procedures and applications, it is a valuable and unique reference tool for everyone interested in formate fluids.
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Part A: Chemical and physical properties
Section A1 describes the basic chemical properties of sodium, potassium and cesium formate brines and their blends. This includes properties such as molecular formula, molecular weight, crystal structure, solubility, solution density, antioxidant properties and water-structuring properties.
Section A2 presents mixing tables for single-salt formate brines and powders, along with blending tables for cesium and potassium formate brines. Measured PVT data for single-salt potassium formate brines and cesium/potassium formate brine blends are tabulated. A model is presented that converts surface density at any temperature to the equivalent density of the brine at standard conditions.
Section A3 presents measured water activity data for sodium, potassium and cesium formate single-salt brines and their blends. The boiling points for sodium, potassium and cesium formate single-salt brines and cesium/potassium formate brine blends are also presented, along with vapour pressure.
Section A4 presents brine viscosities for sodium, potassium and cesium formate single-salt brines, and blends of cesium and potassium formate brines. Brine viscosity has been measured as a function of temperature and brine density for both single-salt brines and blends.
Section A5 presents measured crystallisation temperatures for sodium, potassium and cesium formate single-salt brines and cesium/potassium formate brine blends. A specially developed seeding method for formate brines is described. Pressurised crystallisation temperature (PCT) data for formate brines are also presented. Section A5 is currently being updated and a new version will be available for download shortly.
Section A6 describes benefits of the carbonate/bicarbonate buffer addition and demonstrates these under acid gas influx scenarios. Guidelines are also given for how to measure pH in formate brines.
Section A7 presents measured thermophysical data for a series of realistic sodium, potassium and cesium formate brine blends as a function of temperature.
Section A8 presents measured coefficients of friction for sodium, potassium and cesium formate single-salt brines and cesium/potassium formate brine blends.
Section A9 presents measured resistivity for single-salt sodium, potassium and cesium formate brines and blends, along with temperature dependence for a cesium/potassium formate brine blend. Some nuclear properties and sonic-velocity data are also included.
Section A10 presents measured data for water absorption and desorption of cesium formate brine as a function of temperature with and without agitation.
Section A11 presents results of radioactivity detection tests on standard samples of cesium formate brine, showing that they only contain the stable 133Cs isotope, which is naturally present in the pollucite ore. Measurement results are also shown for potassium formate brine.
Section A12 presents results of several tests completed on formate brines and drilling fluids, which try to predict the exact conditions required for formates to biodegrade and when bacterial growth is inhibited.
Section A13 reviews the hydrothermal behaviour of buffered formate brines and explains why formate brine exposed to hydrothermal conditions in a deep high-pressure well establishes equilibrium with bicarbonate. Analyses of buffered formate brines recovered from HPHT well construction operations are also presented and discussed.
Surface tension is an important property of all water-based fluids used for well construction and intervention operations, and is defined as the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Section A14 contains information on surface tension of sodium, potassium and cesium formate brines. In addition, the effect of some common contaminants and additives on surface tension is evaluated.
Part B: Compatibilities and interactions
Section B1 presents a detailed explanation of how the carbonate/bicarbonate pH buffer protects formate brines from acid gases, such as carbon dioxide and/or hydrogen sulfide, and explains how formate brines are naturally protected against damage caused by oxygen.
Section B2 presents measured solubility data for methane (CH4) and carbon dioxide (CO2) in a blended cesium/potassium formate brine as a function of temperature and pressure, which shows that solubility of these gases in formate brines is very low.
Section B3 presents a simple analytical model that shows how reservoir gases diffuse through formate brines, along with some simple examples of the model’s use.
Section B4 presents possible compatibility issues between formate brines and other fluids that they may come in contact with on the rig or in the well. These are halide brines, oil-based drilling fluids, synthetic-based drilling fluids, base oil, seawater, well treatment fluids, glycols and methanol.
Section B5 presents a thorough review of commonly used drilling and completion fluid additives and their compatibility with formate brines. Additives include biopolymers, synthetic polymers, clays, lubricants, weighting material, corrosion inhibitors, biocides, H2S scavengers, antioxidants, oxygen scavengers and defoamers.
As metal compatibility research is still ongoing, section B6 of the manual has yet to be produced. A report prepared in a separate metal compatibility review of formate brines is available however. Please note that this report is not a live document with regular updates.
Section B7 summarises the results from a variety of elastomer compatibility tests performed on formate brines, along with some general guidelines and recommendations.
Section B8 studies the available data for formate brines and their compatibility with cement, particularly for thickening time, compressive strength and rheology. It ends with recommendations for brine validation, as well as use of spacer fluid and additives in field operations.
Section B9 presents the results of compatibility tests with formate brines and a variety of other materials such as glass, tank linings, subsea control fluids, thread compounds, flowline gate sealant, proppants and pipe-liner materials.
Section B10 explains why formate brines are unlikely to cause any formation damage and details how coreflood testing with formate brines can become meaningless. A coreflood test method is recommended that differentiates between reduced return permeability due to increased water saturation in the core plug and any permanent damage to the core. Lastly, a thorough literature review is presented on well cleanups after drilling and/or completing with formate fluids.
Section B11 explains the mechanisms involved in borehole instability and how formate brines can prevent this from happening. Methods for testing borehole stability are described and results of shale stability testing in formate brines are shown. In addition, relevant field experience with formate brines published in the public domain is reviewed.
Section B12 reviews what is known about the solubility of minerals and salts in formate brines. The unique ability of buffered potassium formate brine to dissolve alkaline earth metal sulfates, such as barium sulfate, is explained and its potential application as scale dissolvers or scale inhibitors is also discussed.
Section B13 presents some measured hydrate equilibrium temperatures in formate brines and compares them with those of well-known hydrate inhibitors such as MEG, MEOH and calcium chloride.
Part C: Formate field procedures and applications
Section C1 presents analyses of the complete life cycle of a high-density formate brine fluid, including supply, application and return. Detailed guidelines for planning and preparation, supply, rig storage and surface handling, wellbore operations, sub-surface exposure, brine recovery and return, and finally brine reclamation are provided.
Section C2 lists the standard recommended tests for brines (API RP 13J) and water-based drilling fluids (API RP 13B-1), specifying which tests are recommended for formate fluids and which are not. Full descriptions of the methods unique to formate fluids or modified for use with formate fluids are provided.