Effects of Thickening Time on the Application of Cement Slurry for High Pressure /High Temperature Drilling.

High pressure/High temperature operations remain a high challenge for the industry as deeper reservoir operations are pursued around the globe. In addition to deeper depths, an increasing number of wells are still being drilled and completed in much more hostile down-hole environments. Though high pressure/high temperature wells have always presented drilling challenges, their operations continued to remain very high as the vast reserves of hydrocarbon promised to bridge the gap between demand and supply for energy. The world’s energy demand is rising and favorable economics have allowed oil companies to continue to prospect and drill in these more challenging areas that are actually prone to high pressures / high temperatures than ever before. This paper addresses some of the challenges relative to cement slurry designs that requires careful engineering practices and needs proper cementing operations and optimization. It presents a simulation study using retarder sensitivity to select thickening time, optimize cement properties and also predict the subsequent HPHT sensitivity on cement slurries. The results showed that the modified Magnesium Oxide(mixture of water-glass and magnesium oxide) was best for slurry design for high pressure/high temperature which gave tighter matrix of cement paste. The application of retarder reduced the thickening time but the Water-Glass Solution improved the Magnesium Oxide cement thickening time, indicating that thickening time was dependent on time of exposure and on temperature. The rheological properties of the slurry showed that at HPHT, there were decreases in plastic viscosity, gel strength and the yield point. The study therefore determined one of the best cement slurry design practices for different down-hole applications in HPHT wells. KEY WORDS : Cement slurry, Thickening Time, Modified magnium Oxide,High temperature/High Pressure

Evaluating the Efficiency of Nigerian Local Bentonite as an Extender in Oil Well Cementation

Nigerian local Bentonite has been in use as an extender in cementing operations since 2003 but has not been widely accepted because of some of its effects and challenges on most of the cement properties. This study is on the experimental and economic evaluation of the effect of Nigerian local bentonite obtained from Awkuzu in Anambra state and the imported bentonite on fresh and salt water cement slurry. The experimental test were basically on the thickening time and the ultrasonic compressive strength.  Both local and foreign  bentonites proved effective in fresh  water  cement slurries and can  be used interchangeably except in cases where higher Plastic Viscosity (PV) and Yield Point (YP) are required .The foreign bentonite proved more effective under this high rheological properties for the same concentration with the local bentonite . In the  salt water cement slurries both local and foreign bentonite were not fully effective, but the local bentonite responded better in the case study  design in terms of  rheology and free fluid tests.  For the  economic  evaluation, a case study of a project involving the 13 3/8 inch  casing cementing operation was  simulated  using fresh water cement slurry. The foreign bentonite contributed 21% to the overall cement slurry cost while local bentonite contributed  2%.leading to  a total savings of $7,509.85. Therefore , local bentonite could be a more efficient and cost effective means of cement slurry extender if properly managed and evaluated

In vitro antioxidant activity‐guided fractionation of Daucus carota L. seed extract

Daucus carota Linn (carrot) seeds are medicinally useful in the management of diseases including diabetes mellitus. The present study investigates the in vitro antioxidant activities and phytochemical constituents of several fractions from aqueous seed extract of Daucus carota. D. carota seeds (78.8g) were pulverized and dissolved in 400 mL of distilled water for 24 hours. The crude extract obtained (16.4g, 20.8% yield) was partitioned in water/ethyl acetate (3:1) to yield ethyl acetate fraction (6.2g, 37.8% yield) and aqueous ethyl acetate fraction (7.6g, 46.3% yield) which was subjected to column chromatography. Thirteen (13) fractions obtained were evaluated for their in vitro antioxidant activities and screened for phytochemical constituents. The fractions exhibited in vitro antioxidant activities at 2 – 20 μg/mL with 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities (IC50 = 1.38 - 22.96 μg/mL), total antioxidant capacity (IC50 = 1.17 - 3.13 μg/mL) and nitric oxide scavenging activities (IC50 = 3.20 - 20.72 μg/mL). Fractions 4 – 8 expressed promising in vitro hydrogen peroxide (H2O2) antioxidant activities with IC50 comparable with that of ascorbic acid and butylated hydroxytoluene. The phytochemical screening of fractions 4 – 8 revealed the presence of alkaloids, flavonoids, and phenolics, which could be responsible for the antioxidant activities. The results suggest that fractions obtained from Daucus carota L. seed extracts possess significant antioxidant potential