Fields in offshore Mexico present different challenges to maximizing resource recovery due to the reservoir characteristics and completion configurations. Acidizing of high temperature (HT) dolomitic reservoirs (290 °F/143 °C) in the maritime fields represents the primary stimulation option due to existing well parameters restricting treatment designs to matrix rate conditions. Acidizing treatments are typically based on HCl and organic acids and for the first time a multifunctional, low viscosity, retarded HCl acid is also available. Laboratory wormhole tests were conducted for matrix injection but also in a pseudo-acid fracture condition (split-core) in order to establish feasibility for future stimulation designs. Three acid blends were used, a blend of organic acids (OA), a mixture of HCl and organic acid (HA), and a polymer free retarded HCl acid (HRMA). The cores tested correspond to a particular well and X-ray Diffraction (XRD) analysis confirms it is >98% dolomite. CT imaging corroborates the heterogeneous permeability due to primary and secondary porosity systems (5% – 10% and 10% – 15%). The pore volume breakthrough of each acid blend was determined for two cores of similar porosity under same constant injection rate. Results indicate the organic acids blend (OA) can have better injectivity when flow rate is much higher than the HCl/Organic acid (HA) blend. A core with 10X lower permeability (0.1 – 0.5 mD) was tested with new Retarded HCl acid (HRMA) using same injection rate as the other acid blends. Results indicate that Retarded HCl (HRMA) does not cause core facial dissolution under unoptimized injection rate. The wormhole patterns generated for the HCl/Organic acid (HA) blend show good distribution and for Retarded HCl (HRMA) show enhance acid containment (less ramification). Both HCl acid blends (HA and HRMA) are suitable for dolomitic acidizing under different injection rates, while the purely organic acid blend is more adequate for high rate injection. Notably acidizing of dolomitic reservoirs can be highly efficient under optimized conditions and future work with non-retarded and retarded acids can systematically drive pumping engineering designs. The Retarded HCl acid (HRMA) has multifunctional properties including scale inhibition and lower HCl reactivity.
Acidizing and acid fracturing techniques are routinely used in two important formations in the marine regions of Mexico, the Jurassic and Cretaceous formations. These formations are naturally fractured carbonate and dolomite reservoirs having a permeability in the range of 0.19 to 22 mD, porosity from 2.8 to 6%, approximate bottomhole temperature (BHT) up to 177°C, pressure (BHP) of 10,374 psi, and a crude of 45° API. Using acid fracturing techniques helps improve the development of these assets. This paper shows the results of more than 40 acid fracturing operations performed in recent years. Depending on the productivity evaluation, wells belonging to these assets are stimulated as part of the completion stage. Because of their low permeability, a common approach is to perform an acid fracturing operation. As a first evaluation, a minifrac test is executed to obtain the necessary data to calibrate the acid fracturing simulation model. After this step is performed, the acid fracturing design is evaluated. Generally, a sustained production acidizing technique is used for conductivity enhancement and closed-fracture acidizing is also included as a tailored treatment with an all seawater-based acidizing system. For these operations, an average five-fold increase in oil production has been observed after treatment. In some cases wells in the completion stage, having no production before treatment, delivered up to 7000 BOPD after treatment. In these low-permeability assets, the post-fracturing response shows good results in general terms, increasing final conductivity in the near-wellbore area, and improving the production in these wells. The fracture gradient observed varies from 0.715 to 0.981 psi/ft with an average minimum stress of 13,670 psi. To perform the acid fracturing treatments, an average of 6400 hydraulic horsepower (HHP) must be available, with up to 13,400-psi surface pressure observed. As such, a stimulation vessel is necessary in all operations, applying a 26-bbl/min average pumping rate. Globally, acid fracturing treatments are a common stimulation technique. This study shows that stimulating proper candidates in Mexico using acid fracturing significantly helps increase production, which may be relevant for the exploitation of new areas where fracturing has not been implemented.
Removal of wellbore scale from downhole equipment continues to impact well economics due to productivity losses and asset maintenance. The use of first-of-its-class calcium sulfate (CaSO4) scale dissolver in high producing offshore wells equipped with electric submersible pumps (ESP) is presented. The efficiency of the new fluid surpasses the performance of established dissolvers since it does not require long shut-in periods. Anhydrite (CaSO4) scale dissolution and removal can be accomplished with a simple treatment fluid employing a formulation that has been field-proven to restore production and protect downhole equipment in a time-efficient manner. Mineral anhydrite and wellbore scale samples were tested with the dissolver formulation at 200°F (93.3°C), under static conditions for one hour. Dissolution efficiencies greater than 94% were a requirement. Fluid compatibility with metallic and non-metallic components in the wellbore were assessed at bottom hole static temperature (BHST) conditions for a period of 24 hours. The fluid was deployed from a stimulation vessel at a pumping rate from 1 to 5 bpm. A small volume pill of 5 m3 on average was pumped in at least 20 wells, through the production tubing to the ESP and was allowed to soak for 1 hour. Wells were immediately opened to production after a 1-h soak period. Minimizing the non-productive time incurred when long soak periods are required has been attained with the use of the new dissolver fluid, leading to greater efficiencies associated with CaSO4-type scale removal. ESP temperature was monitored and reduced by 13°F (7.2°C) after treatment, similar to temperatures before scale build up. After the treatment, the results show a 1.125-fold increase in oil production. The fast-acting formulation exceeds 90% dissolution efficiency within one hour and improves operations by using a fluid that is non-corrosive to downhole materials in a one-stage removal package. The dissolver formulation provides dissolution of anhydrite at 200°F in ESPs. The fast acting dissolver is delivered as a single fluid package and eliminates the need for separate fluid stages as well as the use of incompatible fluids. Anhydrite scale dissolution and removal can be accomplished with a simple treatment fluid and extend the life of the ESP.
Huntingtons disease (HD) results from a CAG repeat expansion in the gene for Huntington (HTT) resulting in expansion of the polyglutamine (Q) tract in the mutant protein (mHTT). Synaptic changes are early manifestations of neuronal dysfunction in HD. However, the mechanism(s) by which mHTT impacts synapse formation and function is not well defined. Herein we explored HD pathogenesis in the BACHD and the deltaN17-BACHD mouse models of HD by examining cortical synapse formation and function in primary cultures maintained for up to 35 days (DIV35). We identified synapses by immunostaining with antibodies against pre-synaptic (Synapsin 1) and a post-synaptic (PSD95) marker. Consistent with earlier studies, cortical neurons from both WT and the HD models began to form synapses at DIV14; at this age there were no genotypic differences in synapse numbers. However, from DIV21 through DIV35 BACHD neurons showed progressively smaller numbers of synapses relative to WT neurons. Remarkably, BACHD synaptic deficits were completely rescued by treating cultures with BDNF. Building on earlier studies using reagents inspired by the chaperonin TRiC, we found that addition of the recombinant apical domain of CCT1 partially rescued synapse number. Unexpectedly, unlike BACHD cultures, synapses in deltaN17-BACHD cultures showed a progressive increase in number as compared to WT neurons, thus distinguishing synaptic changes in these HD models. Using multielectrode arrays, we discovered age-related functional deficits in BACHD cortical cultures with significant differences present by DIV28. As for synapse number, BDNF treatment prevented most synaptic deficits, including mean firing rate, spikes per burst, inter-burst interval, and synchrony. The apical domain of CCT1 showed similar, albeit less potent effects. These data are evidence that deficits in HD synapse number and function can be replicated in vitro and that treatment with either BDNF or a TRiC-inspired reagent can prevent them. Our findings support the use of cellular models to further explicate HD pathogenesis and its treatments.
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