EXPERIMENTAL STUDY OF HOLE CLEANING PERFORMANCE OF UNDERBALANCED DRILLING AT DOWNHOLE CONDITIONS

Underbalanced drilling is one of the most widely used drilling technologies while drilling poor permeability, low pressure and depleted reservoirs. Advantages inherent in application of this drilling technique which are major factors affecting cost, time and drilling quality can be significantly hindered due to poor hole cleaning performance. Experimental study of hole cleaning performance in underbalanced drilling at downhole temperatures260C, 400C and 600C   and water influx of  0.25m3/s in a simulated vertical well using gasified mud  was carried out.  Results showed that increasing down-hole temperature by 340C above 260C (ambient temperature) caused 42% and 21.6% increase in annular concentration at flow rates 0.3m3/s and 1.6m3/s respectively. Increasing mud flow rate by 1.3m3/s above 0.3m3/s at  downhole temperatures:260C and 600C and water influx at 0.25m3/s caused 68% and 47.6% decrease in annular cutting concentration. Increase in downhole temperature at constant flow rate resulted in poor hole cleaning performance due to increased in annular cutting concentration. Also, increasing mud circulation rate at a given downhole temperature led to an improved hole cleaning performance due to decrease in annular cutting concentration.  Sensitivity   studies of effect of  mud viscosity, gas/liquid ratio, cutting density and water influx   at  400C  revealed that increasing mud viscosity and gas/liquid ratio  significantly improved the hole cleaning performance while cutting density and water influx cause poor hole cleaning. However, effect of increasing water influx becomes problematic only when the volume is excessively high and miscible with the circulating mud. http://dx.doi.org/10.4314/njt.v35i2.1

Performance of cowpea varieties under Striga gesnerioides (Willd.) Vatke infestation using biplot analysis

Published online: 10 October 2017Striga gesnerioides (Willd) Vatke, is a major destructive parasitic weed of cowpea (Vigna unguiculata (L.) Walp.) which causes substantial yield reduction in West and Central Africa. The presence of different virulent races within the parasite population contributes to significant genotype × environment interaction, and complicates breeding for durable resistance to Striga. A 3-year study was conducted at three locations in the dry savanna agro-ecology of Nigeria, where Striga gesnerioides is endemic. The primary objective of the study was to identify cowpea genotypes with high yield under Striga infestation and yield stability across test environments and to access suitability of the test environment. Data collected on grain yield and yield components were subjected to analysis of variance (ANOVA). Means from ANOVA were subjected to the genotype main effect plus genotype × environment (GGE) biplot analysis to examine the multi-environment trial data and rank genotypes according to the environments. Genotypes, environment, and genotypes × environment interaction mean squares were significant for grain yield and yield components, and number of emerged Striga plants. The environment accounted for 35.01%, whereas the genotype × environment interaction accounted for 9.10% of the variation in grain yield. The GGE biplot identified UAM09 1046-6-1 (V7), and UAM09 1046-6-2 (V8), as ideal genotypes suggesting that these genotypes performed relatively well in all study environments and could be regarded as adapted to a wide range of locations. Tilla was the most repeatable and ideal location for selecting widely adapted genotypes for resistance to S. gesnerioides