Closed-loop feedback control of smart wells for production optimisation using self-potential measurements

Closed-loop ‘reactive’ feedback control techniques used for smart well optimisation, triggered by changes in flow (such as unwanted water production) measured at the well can increase the net present value (NPV) and mitigate reservoir uncertainty, as opposed to model-based control strategies, which use models that are rarely predictive at their spatial and temporal scales required to identify optimum control actions. However, the drawback faced with closed-loop ‘reactive’ feedback control is that control actions are only taken after adverse changes of flow occur at the well. We present a modified close-loop ‘proactive’ feedback inflow control approach based on near-well, downhole measurements of self-potential (SP) and quantify the potential benefit of this approach in different well and reservoir settings during waterflooding or aquifer support production. The measurement of SP signals downhole in production wells is an encouraging technique that can be used to image waterfronts and has the potential of detecting water encroachment tens to hundreds of meters away from the well. SP signals arise in order to preserve electrical neutrality when charge separation arises due to gradients in pressure, temperature and chemical concentration of the reservoir brine phase. These gradient effects are commonly encountered during waterflooding processes and can be assessed numerically to predict the SP generated downhole in oil production wells. The numerical modelling of SP can be used as a cheap alternative to carrying out actual field experiments and serve as a proxy for predicting the SP measurements taken during waterflood production. Hence, a closed-loop ‘proactive’ feedback control strategy triggered by downhole SP measurements is developed. We use the NPV of the production wells to measure and compare the performance of the closed-loop feedback control in two different synthetic production cases; the first production case is a simple thin oil-column reservoir with production enabled by a single long horizontal well, and the second more realistic SPE Brugge field model, with production enabled by 20 production wells. The results observed are promising, and suggest that closed-loop control on the basis performance of downhole SP feedback can yield increased gains in NPV, by delaying the production of unwanted fluids compared with water-cut monitoring. These gains are also observed even if the reservoir lies outside the range predicted by reservoir models. Finally, we investigate the potential utility of SP monitoring in analogue real field applications. Overall the results are promising and suggest that SP measurements can be useful in making critical decisions in real field exploration and production applications, and other non-oil related fields such as saline intrusion monitoring in coastal aquifers.Open Acces

Serum Biochemical Changes in Alloxan-induced Diabetic Rats and Ameliorative Effects of Moringa oleifera and Morinda lucida Leaf Extracts

This study evaluated the antidiabetic properties and biochemical changes in alloxan-induced diabetic rats treated with Moringa oleifera and Morinda lucida leaf extracts. The acute toxicity values of the extracts were determined before evaluating their antidiabetic effects in 7 groups of 4 rats each. Rats in groups 1-6 were made diabetic via a single injection of alloxan monohydrate (160 mg/kg i.p). Animals whose blood glucose levels rose to 200 mg/dl and above were considered diabetic and used for the study, but group 7 was the normal control. Groups 1 and 2 received 500 and 250 mg/kg of M. oleifera extract, respectively, while groups 3 and 4 received 500 and 250 mg/kg of M. lucida extract, respectively. Group 5 received 3 mg/kg of the standard drug (Daonil), while groups 6 and 7 were the diabetic and normal control groups, respectively. Treatment lasted for 21 days and was administered orally. The phytochemical screening results showed that each of the extracts was rich in phytochemical agents. Higher amounts of flavonoids and terpenoids were found in M. oleifera, while M. lucida had higher phenols and saponins. LD50 value obtained for each extract was above 5000 mg/kg. Results of the antidiabetic study indicated that the extracts significantly brought down glucose levels in the test rats (p<0.05) when compared with the diabetic control. Treatment also restored elevated lipids values, liver function, and renal function parameters in the diabetic rats. The decreased glutathione, catalase, and superoxide dismutase activities and increased lipid peroxidations resulting from diabetes mellitus induction were also significantly corrected following extracts administration when compared with the diabetic control (p<0.05). Our findings show that Moringa oleifera and Morinda lucida extracts may be safe for use in the management of diabetes mellitus and its associated biochemical complications

Numerical modelling of self-potential in subsurface reservoirs

We report a new, open-source, MATLAB-based 3D code for numerically simulating the self-potential (SP) in subsurface reservoirs. The code works as a post-processor, using outputs from existing reservoir flow and transport simulators at a selected timestep to calculate the SP throughout the reservoir model. The material properties required to calculate the SP are user defined and may be constant or vary in each cell. The code solves the equations governing flow and transport of electrical charge and global charge conservation using a control-volume-finite-difference scheme. Electrical currents associated with the SP may spread beyond the reservoir model domain, and the code allows for the domain to be extended vertically and laterally to account for this. Here, we present the governing equations and the numerical method used and demonstrate application of the code using an example in which we predict the SP signals associated with oil production from a subsurface reservoir supported by water injection

Anthelmintic activities of Polyalthia longifolia leaf and stem bark extracts in Heligmosimoides bakeri infected mice

Polyalthia longifolia is used traditionally to manage intestinal worm infections. In this study, the anthelmintic activities of the leaf and stem bark extracts were evaluated in Heligmosimoides bakeri infected mice. Extracts were first subjected to phytochemical and acute toxicity (LD50) tests. For the anthelmintic study, in vivo and in vitro models were adopted. In the in vivo study, groups 3 – 6 of infected mice were assigned specific extract treatments, while groups 1, 2 and 7 were the normal, negative and standard (albendazole treated) groups respectively. Egg count was determined every 3 days during treatment. In the in vitro model, the extracts were applied to the worms in&nbsp; Petri dishes before larvae counts. Results obtained showed the presence of significant amounts of alkaloids, flavonoids, tannins, steroids, terpenes, saponins, cardiac glycosides and phenols in both extracts with LD50 values &gt;5000 mg/kg body weight for both extracts. Result of the in vivo anthelmintic study showed significant fall in egg/larval count in all groups treated with the extracts (p&lt;0.05), as 400 and 800 mg/kg of the leaf extract lowered egg count to 0.60 ± 0.24 and 0.20 ± 0.20 respectively while same doses of the stem bark extract lowered egg count to 0.40 ± 0.24 and 0.20 ± 0.20 respectively, when compared with the negative control group which had a count of 297.80 ± 13.18. Results obtained in the in vitro model also indicated significant vermicidal effect for both extracts. We therefore conclude that P. longifolia may be potential sources of vermicidal agent

Persistence of frequency in gas–liquid flows across a change in pipe diameter or orientation

From a study of the characteristics of structures across a 67/38 mm sudden contraction, using air/silicone oil flows, it has been found that frequencies of the structures (mainly slugs) persist across the contraction. This is in contrast to the velocities and lengths which increase as they move into the smaller diameter pipe. These observations were found for both vertical and 5° upward orientations. A similar persistence of frequency has been found from four other sources in the literature: a vertical (gradual) contraction; a horizontal Venturi; and two cases of horizontal pipe, 90° bend and vertical riser combination. The latter were at two contrasting conditions: (i) at atmospheric pressure with air/water in small diameter (34 mm) pipes; (ii) at 20 bar in larger diameter pipes (189 mm) using nitrogen and naphtha