Two hydrophobic vinyl saccharide monomers based on D‐glucose and D‐fructose were polymerized by employing the reversible addition‐fragmentation transfer (RAFT) miniemulsion polymerization technique to prepare well‐designed glycopolymers. Three dithiobenzoate‐RAFT agents [SC(Ph)SR], 1‐phenylethyl dithiobenzoate (PED), 2‐phenylprop‐2‐yl dithiobenzoate (PPD), and 2‐cyanoprop‐2‐yl dithiobenzoate (CPD), were used to control the growth of polymer chains. The best results were obtained in the presence of the PPD‐RAFT agent and the formed polymers have polydispersity index's (PDI) lower than 1.15. Under adequate miniemulsion polymerization conditions, a glycopolymer with PDI of 1.1 and molecular weight of 5 × 104 g/mol has been successfully synthesized in a short reaction time of 100 min. Furthermore, some block copolymers containing saccharide segment with butyl or methyl methacrylate were prepared. Copyright © 2007 John Wiley & Sons, Ltd.
Barite has been used to increase the density of drilling fluids (DF) since 1922. However, circumstances & needs are changing: The API has recently introduced a new standard for 4.10 sg barite in recognition of diminishing supplies of readily available barite that meet API’s standard minimum density specification of 4.20 sg - high quality barite is running out. The search for new hydrocarbon resources to replace reserves has resulted in more difficult drilling conditions & fluid requirements e.g. deepwater, ERD, HPHT etc., where ECD management, sag control & formation damage mitigation are critical to success. Alternative weighting materials (WM) such as manganese tetraoxide, treated micronized barite & cesium formate have been successfully used to handle many of the problems mentioned, but they are expensive & not produced in large volumes. Therefore, their application tends to be restricted. There is, therefore, a need for alternative weighting materials capable of providing better functionality than barite, but available in sufficient volumes to meet requirements & be competitively priced. This paper describes a new micronized, weighting agent, suitable for use in drilling & completion fluids, which offers significant advantages in the control of ECD, sag & formation damage. It is denser than barite, acid soluble, available in large volumes of > 100,000 tpa and is significantly cheaper than the current, high-end weighting materials. Test results are given showing stable fluids with low plastic viscosity, gel strengths & sag, even under HPHT conditions, for both aqueous & non-aqueous based fluids. The material has an excellent HSE profile & is soluble in oilfield acids. Accordingly, it provides a viable alternative product, intermediate between barite & the more expensive weighting materials.
Hydraulic fracturing is used extensively to develop oil and gas wells in both high and low-permeability formations. Biopolymer-based fluids, including guar or guar derivatives, constitute the majority of polymers in fracturing fluids. These polymers cause formation damage, which is a serious problem on production enhancement. Therefore, the search for an alternative to guar is meaningful to the oil industry. In this paper, a novel viscosifier (V1) was developed to prepare fracturing fluids. The rheological properties and proppant suspending ability of V1-based fluid have been studied with the effects of viscosifier concentration, temperature, and salts. Formation damage of the new type of hydraulic fracturing fluid in sandstone has been evaluated and compared to guar, hydroxypropyl guar (HPG), and viscoelastic surfactant (VES) fluids. The effects of temperature, viscosifier type, concentration, and formation permeability were investigated. The regained permeability of sandstone cores (expressed as a percentage of the initial permeability) was used to quantify the damage degree in coreflood tests. The viscosity measurements have shown that V1-based fluids were stable up to 350°F with a high tolerance to KCl and CaCl2. Moreover, V1-based fluids had a good proppant suspending ability at 75 and 250°F, which out-performanced guar-based fluids. Coreflood tests were run using Berea and Bandera sandstone cores. As for V1 fluids, the regained permeabilities of the cores were 88% or higher of the initial permeabilities, suggesting that V1 caused a slight damage. However, guar and HPG fluids caused much more damage than V1 fluids under same conditions. The effects of temperature, viscosifier concentration, and formation type were different for guar-based fluids from V1 fluids. The external filter cake was formed when the V1 fluid was injected; however, no external filter cake was found for guar, HPG, or VES. The filter cake could be removed by injecting 5 wt% KCl brine in the opposite direction. It was the first time to use this new cellulosic viscosifier in hydraulic fracturing fluids. The new type of fracturing fluid has better thermal stability and proppant suspending ability than guar-based fluids under the same conditions. Moreover, high regained permeability of sandstone cores can be maintained when treated by the new fracturing fluid.
Ilmenite (FeTiO 3 ) was first introduced as a weight material in the North Sea area in the early 1980's. The quality of ilmenite suitable for drilling fluids was continuously improved to meet the drilling criteria. Ilmenite as a weight material offers many benefits over API barite such as high density (4.6SG), mineral hardness (6 Mohs), low heavy metals content, acid solubility and sustainability due to the large reserves.Currently there are certain drilling areas such as narrow pressure margin wells, HPHT wells, deep water, ERD, and slim hole, where API barite may not offer the required performance. For those wells a controlled rheology and minimal sag is the key to success and a specialty weight material can provide this. To fulfill such needs a micronized ilmenite grade (5µm) has been developed for use as a weight material for drilling fluids. The paper will show the testing of the new grade in both aqueous and non-aqueous drilling fluids. High temperature dynamic sag and filtration results will be presented. Acid solubility in hydrochloric acid will be highlighted. The new grade shows excellent dynamic sag, stable rheology and high acid solubility, which are very useful for many drilling operations particularly deep offshore drilling. On a top of the high performance this new advanced material is a cost-effective solution for some of the high costly drilling challenges.
Dispersants are widely used in drilling fluids to prevent solids flocculation and to control the rheological properties of the fluids. There is high demand for effective, thermally stable and environmentally friendly dispersants for HPHT drilling fluids. This work was undertaken to investigate the use of environmentally friendly dispersants in HPHT aqueous drilling fluids containing manganese tetroxide (Mn3O4) as the weighting agent. The dispersants were chosen because they are non-toxic to aquatic organisms and biodegradable. The effects of cement, rock salt and clay particles as contaminants on the dispersant performance and the fluid properties were investigated. The dispersants were lab tested in high density fluids of 2.1 g/cm3 at a temperature of 200°C and pressure of 500 psi. The fluids were analyzed before and after heat-aging using rheometer, sag test, light scattering, and HPHT fluid loss. Out of over 100 dispersants tested, two dispersants showed best performance in controlling the flow behavior of the fluids in the presence of contaminants. Dispersant A is a synthetic copolymer of maleic anhydride and acrylic acid and dispersant B is an anionic lignosulfonate. They are compatible with water based drilling fluid system having manganese tetroxide as the weighting agent (SG = 2.1) and thermally stable (150-250 °C). Both dispersants lowered the rheology including plastic viscosity and yield point before and after heat aging (200°C) when compared to blank. They show also lower sag and fluid loss values in the presence of contaminants and lowered the filter cake thickness.
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