Summary: Scale formation in downhole tubular-flow passages can cause partial to complete plugging that will affect production or injection rates adversely. In an intelligent-well completion in which the interval-control-valve (ICV) opening must be changed to control flow rate, the completion will become ineffective if plugging of clearances prevents valve actuation. To mitigate these problems, a method to predict the potential rate of scale formation under realistic conditions has been developed. This empirical method allows prediction of tool performance under scale-forming conditions for downhole applications, and uses chemical data and flow fields generated by computational-fluid-dynamics (CFD) models for downhole tools. Chemical data are obtained from laboratory tests on coupons by use of brines matching the chemistry of connate fluids. Tests were conducted in a high-pressure, corrosion-resistant vessel over a range of high pressures (100 to 10,000 psi) and high temperatures (75 to 150 °C) to simulate downhole well conditions. Two test sets were conducted, each with fluid at rest and with an impeller generating low velocity in the reaction vessel, ranging from 4 hours to 4 days, with scaling rates determined from coupon-weight gain. Concentrations in the range of 50 to 125% of the typical connate-fluid concentration were used. The weight-gain data obtained from the coupon tests and from a tube-plugging test were used to develop an empirical model for scale-growth rate at a given point on a solid surface with pressure, pressure gradient, temperature, fluid velocity, and brine concentration as independent variables. Artificial-intelligence methodology was used to develop this model, which can be used to predict the scale-growth rate for any arbitrary geometry. By use of the internal geometry of any tool to be modeled, a CFD model is prepared and the pressure, fluid velocity, and pressure-gradient data are generated for the entire internal solid surface of the tool for a given flow rate through the tool. These data are fed into the empirical model to calculate the scale-growth rate, which is integrated to obtain scale thickness at each point of the internal solid boundary. To verify accuracy, scale formation in a 4.5-in. ICV was predicted at high-pressure, high-temperature conditions at a low flow rate. Laboratory tests on the valve matched the model predictions well enough, which enabled Petrobras to design a better completion and fluid-handling system for a presalt well.

Stereotactic radiosurgery (SRS) poses a minimal but important risk for tumour transformation, typically occurring 8–10 years after the treatment. Malignant peripheral nerve sheath tumour (MPNST) is the most common tumour arising from a vestibular schwannoma treated with SRS, with only 14 cases previously reported. We present the fifteenth case and describe its evolution and clinical course. A 56-year-old man without a history of neurofibromatosis was diagnosed 9 years prior with a vestibular schwannoma. SRS to the residual tumour was given 3 months later. During the current hospitalisation, he was reoperated where histology confirmed a MPNST. All 15 MPNST cases were analysed, showing a 77% female predominance presenting a malignant transformation at a mean age of 51. The diagnosis was made at a mean time of 74 months after SRS. The mean survival time after diagnosis was 16 months. MPNST arising from benign vestibular schwannoma after SRS treatment is an uncommon but devastating complication.

Colloid cysts of the third ventricle are rare lesions. To our knowledge, only 23 familial cases of colloid cysts have been reported in the literature. The country of origin of the patients with familial cases had not been previously studied as a group. A 49-year-old female patient from Puerto Rico and her 21-year-old daughter underwent surgical resection for colloid cysts within a period of 5 years. The daughter presented with symptomatic hydrocephalus, while the mother only had mild chronic headaches. The occurrence of a colloid cyst in this family prompted us to perform a literature review and tabulate all the familial cases. This report presents the 24th case of a familial colloid cyst, and the fourth involving a mother and daughter. Australia is the country with the largest amount of reported cases. For smaller countries such as Sweden and Finland, two cases had been reported for each of them. Due to the unlikely probability of familial colloid cyst occurring at random, a genetic component is likely to be involved. The occurrence of several reports from patients from Australia, Finland, Sweden, and Puerto Rico where the population is smaller or more segregated may also suggest a genetic inheritance. Screening of first-degree-related subjects is recommended for families in which two or more members are affected. The presence of a colloid cyst in a twin mandates neuroimaging in the other twin, as there are five familial cases in twins reported in the literature.