As the oil industry continues to operate in more complex and ultrahigh temperature environments scale control becomes an ever increasing challenge. Scale inhibitors are being pushed to their operational limits and start to lose their efficiency against both calcium carbonate and calcium sulphate scales at >400°F. It is therefore essential to develop the next generation scale inhibitor to work effectively against scale in harsh, high temperature environments such as steam floods and gas wells. In this study, details will be provided on the thermal stability test of a novel, biodegradable phosphonate scale inhibitor at temperatures 300°F and 400°F at two pH values, pH 4.0 and pH 6.0. Bottle tests on calcium carbonate and calcium sulfate were conducted with the thermal-aged phosphonate for their inhibition. Dynamic tube blocking tests were also conducted for calcium carbonate and calcium sulfate inhibition at 392°F to demonstrate the performance of the inhibitor. The new phosphonate scale inhibitor has also been designed to be biodegradable and it can be deployed by both continuous injection and scale squeeze treatment which is an advantage compared to polymers as they are often less suitable for high temperature scale squeeze treatments. Careful consideration was also given in the molecular design process for high calcium tolerance and details of brine compatibility at high temperature will be provided. This paper presents details of the evaluation of a biodegradable, thermally stable and calcium tolerant phosphonate scale inhibitor for both calcium sulphate and calcium carbonate scale control in ultrahigh temperature environments at ~400°F. In addition, the environmental test data will be discussed along with details of a field example of continuous downhole deployment of the new phosphonate scale inhibitor for calcium carbonate scale control in a high calcium brine (30,000 mg/L).

The formation of silica and silicate scales caused troublesome issues in various water-handling systems, including steam generators, geothermal wells, and waste-water disposal systems. Recently, a produced water with over 300 ppm of silica, and a spent brine off the strong acid cation (SAC) softeners containing high levels of calcium (Ca), barium (Ba), and magnesium (Mg) were commingled in the production wells. The mixing of these two waters induced silicate as well as other scales, including calcite, barite, etc. In order to provide effective scale inhibition when these waters are mixed, effective scale inhibitors for both silicate and other scales were requested for evaluation. In this paper, scale inhibitor chemistries for preventing both silica/silicate and other scales were reviewed and the possible synergistic effects were assessed by Design of Experiment (DOE) software. DOE is a systematic method to determine the relationship between several factors, i.e. various chemistries and the performance of formulations under designed application conditions. Selected chemicals were formulated for control of both silica/silicates and other scales, and their performances were evaluated by a Kinetic Turbidity Test (KTT). The KTT is a novel laboratory test method using an Ultraviolet-Visible (UV-Vis) spectrophotometer to monitor the formation of scales at various dosages of tested products. Bottle tests were also conducted for the comparison of inhibition performance. Based on the lab testing results from the KTT and the bottle tests, the combined products exhibited good scale inhibition performance for both silicate and other scales. The product was recommended for field applications. Subsequent field applications of this product have provided the desired scale control. This paper presents the laboratory testing data for scale inhibitor selection for the combination products on both silica/silicate control and other scale control by using the efficient performance evaluation method. It also provides an effective product formulation approach for finding synergetic effects of different products. Successful scale inhibitor implementations in the field applications are also presented in this paper. Both laboratory and field testing results show a good case history for the optimization of the silica/silicate and other scale treatment.

Scale inhibitors are commonly used for mitigating scale deposition risks in many oil and gas wells worldwide. Of the various chemistries used for scale inhibition, much research has gone into the various conditions in which each chemistry performs best (i.e. temperature, brine solubility, salinity, etc.)4-6. Furthermore, it is known that dissolved iron (Fe2+ and Fe3+) can hinder the performance of scale inhibitors, some more than others3. Thus, applying this knowledge we can extrapolate which inhibitor chemistries might perform best under a given set of conditions. This knowledge can then be applied regionally where most production comes from the same or similar reservoirs and production conditions. However, less research has been conducted on the effects of pre-existing iron sulfide deposits on the performance of scale inhibitors. Iron sulfide solids are becoming increasingly problematic in the oil field. The combination of iron sulfide with more conventional scaling deposits and the fact that scale inhibitors are surface active and tend to adsorb onto surfaces can yield very challenging situations. This paper discusses testing conducted on various scale inhibitor chemistries and evaluates how exposure to pre-existing FeS solids may impact performance. The various scale inhibitors were evaluated for inhibition performance against a set of controls (no FeS exposure) utilizing the NACE Standard TM0137-2007 "Laboratory Screening Tests to Determine the Ability of Scale Inhibitors to Prevent the Precipitation of Calcium Sulfate and Calcium Carbonate from Solution (for Oil and Gas Production Systems)" with an additional pre-test procedure to expose scale inhibitors in stock solution to a set weight of reagent grade ferrous sulfide (FeS). Scale inhibitor chemistries evaluated include two polymers (scale inhibitor A and B) and five phosphorous based scale inhibitors (scale inhibitors C through F). The various configurations tested included: scale inhibitors alone, scale inhibitor plus FeS solids, scale inhibitor without FeS plus crude oil, scale inhibitor plus FeS and crude oil. The inclusion of the crude oil allowed an interface for potential micelle interactions. The results indicate scale inhibitors A, C and G were least affected by the presence of FeS with no regard to the presence of crude oil. With this study a scale inhibitor that worked best in the presence of FeS solids for the customer's field in the Permian Basin, where FeS has become an increasing issue, was recommended. This also allowed the customer to treat the FeS solids issue via the method that works best for them.

Free-standing caissons are used for supporting flare pipes and single-well production platforms. However, caissons tend to be flexible and dynamically sensitive, and the static design practice may not be adequate for this type of practice may not be adequate for this type of structure. To assess motion effect on the integrity of the structural system and to quantify the allowable motion for safe operation on board a caisson platform, analytical and experimental studies of platform, analytical and experimental studies of the dynamic behavior of a caisson structure were conducted and are described here. The analytical simulations agree well statistically with The motion measurements. A caisson design procedure considering dynamic effects was developed Design considerations include ultimate strength failure, fatigue failure, excessive motion, and possible damage during installation. A key feature in an effective caisson design is that the upper part of the caisson should be made as small as possible so that wave loading and the caisson period can be minimized The fatigue design procedure was verified with past caisson operational experience. To illustrate past caisson operational experience. To illustrate the procedure, a flare-pipe support caisson in 185 ft of water was designed and analyzed. Introduction Free-standing caissons are used for supporting flare pipes or single-well production platforms. The attractiveness of a caisson structure lies in the potential economy and the short time required for potential economy and the short time required for fabrication and installation. However, a caisson tends to be flexible, and dynamic effects may increase the design requirements from both strength and functional standpoints. To assess the motion effect on the integrity of the structural system and to quantify the allowable motion level for effective operation on board a caisson platform, analytical and experimental studies of the dynamic behavior of a caisson structure were conducted, and a procedure was formulated for designing a caisson considering dynamic effects. Observations from the experimental data and computer simulations of the caisson behavior are described. Verification of the computer simulation and some useful information for developing and using such simulations as well as practical interpretation of the analytical results practical interpretation of the analytical results also are given. Differences between a static design and a dynamic design are illustrated in an example design of a flare-support caisson in 185 ft water. MOTION MEASUREMENT Motion data were taken from a caisson platform offshore Louisiana. General dimensions of the caisson are shown in Fig. 1. SPEJ P. 291

Free-standing caissons are used for supporting flare pipes and single well production platforms. However, caissons tend to be flexible and dynamically sensitive, and the static design practice may not be adequate for this type of structure. In order to assess the motion effect on the integrity of the structural system and to quantify the allowable motion for safe operation on board a caisson platform, analytical and experimental studies of the dynamic behavior of a caisson structure have been conducted and are described in this paper. The analytical simulations check well with the motion measurements in a statistical sense. A caisson design procedure considering dynamic effects has been developed. Design considerations include ultimate strength failure, fatigue failure, excessive motion and possible damage during installation. A key feature in an effective caisson design is that the upper part of the caisson should be made as small as possible so that wave loading and the caisson period can be minimized. The fatigue design procedure has been verified with past caisson operational experience. To illustrate the procedure, a flare pipe support caisson in 185 ft of water has been designed and analyzed. INTRODUCTION Free-standing caissons are used for supporting flare pipes or single well production platforms. The attractiveness of a caisson structure lies in the potential economy and the short period required for fabrication and installation. However, a caisson tends to be flexible and dynamic effects may increase the design requirements from both strength and functional standpoints. In order to assess the motion effect on the integrity of the structural system and to quantify the allowable motion level for effective operation on board a caisson platform, analytical and experimental studies of the dynamic behavior of a caisson structure have been conducted and a procedure for designing a caisson considering dynamic effects has been formulated. Observations from the experimental data and computer simulations of the caisson behavior are described in this paper. Verification of the computer simulation and some useful information in developing and using such simulations as well as practical interpretation of the analytical results are also given. Differences between a static design and a dynamic design are illustrated in an example design of a flare support caisson in 185 feet of water. MOTION MEASUREMENT Motion data were taken from a caisson platform offshore Louisiana. General dimensions of the caisson are shown in Figure 1. Motions of the platform were measured by a self-contained, single-channel vibration monitor. The instrument can only take measurements from one direction at a time. Horizontal motions were measured at the heliport, production deck, wellhead deck, and boat landing. The motions were taken in directions both perpendicular to and parallel to the wave crest. Neither a wave staff nor an anemometer was available at the caisson platform and the sea state and wind velocities were obtained by visual estimation. The environmental conditions, maximum platform accelerations and measured platform periods are summarized in Table 1.