A coupled model of temperature and pressure based on hydration kinetics during well cementing in deep water

Considering the complicated interactions between temperature,pressure and hydration reaction of cement,a coupled model of temperature and pressure based on hydration kinetics during deep-water well cementing was established.The differential method was used to do the coupled numerical calculation,and the calculation results were compared with experimental and field data to verify the accuracy of the model.When the interactions between temperature,pressure and hydration reaction are considered,the calculation accuracy of the model proposed is within 5.6%,which can meet the engineering requirements.A series of numerical simulation was conducted to find out the variation pattern of temperature,pressure and hydration degree during the cement curing.The research results show that cement temperature increases dramatically as a result of the heat of cement hydration.With the development of cement gel strength,the pore pressure of cement slurry decreases gradually to even lower than the formation pressure,causing gas channeling;the transient temperature and pressure have an impact on the rate of cement hydration reaction,so cement slurry in the deeper part of wellbore has a higher rate of hydration rate as a result of the high temperature and pressure.For well cementing in deep water regions,the low temperature around seabed would slow the rate of cement hydration and thus prolong the cementing cycle.

CNPC's New Progress in Well Cementing Techniques

Well cementing is an important step in petroleum engineering territory. Through many years study and research, China Nation Petroleum Corporation(abbreviated as CNPC) has made many good progresses in cementing process, and a series of cementing materials, cementing tools, and associated cementing techniques to them have been developed. Over the recent years, there have been significant improvements in application of single slurry system to super deep well, horizontal well, large displacement well and wells with large temperature span between cementing top and well bottom. Favorable results have been gained in field application of super high density cement slurry system and super low density cement slurry system. Application of conventional cementing tools and accessories has been the matured techniques, and breakthroughs have been made in liner hanger and swellable material.

A comprehensive review of the application of nano-silica in oil well cementing

Oil and Gas Industry is a Multi-Billion Dollar Industry.Drilling a well is costly,right from exploration to drilling and production to Enhanced Oil Recovery(EOR).Nanotechnology has the potential to introduce revolutionary changes in several areas of the oil and gas industry,such as exploration,drilling,cementation,production,EOR,etc.Use of Nanotechnology in the cement slurry can also achieve solutions to some of the problems pertaining to oil well cementation.Nano-silica is a better alternative compared to conventional additives like calcium chloride and silica,because as compared to calcium chloride and silica,the amount of nano-silica to be added is very small.Nano-silica acts as a multi-functional additive.Upon addition of nano-silica to cement slurry,there is a decrease in the thickening time,an increase in the compressive strength,decrease in porosity and permeability within the cement and also a decrease in the fluid loss.Incorporation of nano-silica ensures proper cementation and greater integrity of the well.Nano-silica helps in decreasing the wait on cement(WOC)time and therefore reduces the overall capital cost.Nano-silica is highly recommended for deep offshore wells where high temperature and high pressure are often encountered.This paper discusses the behavior of Nano-silica at high temperatures and also reviews effects of Nano-silica on various properties of cement.

A novel approach to identifying the ultrasonic echoes for inspecting well cementing quality

In this paper, it is presented that an approach based on Continuous Wavelet Thansform(CWT) and Fourier Transform(FT) for identifying ultrasonic echoes in inspecting oil well cementing quality. First, CWT is used to process echo signals. Then spectra of the processing results in some specilic scale-time segments are calculated as pattern features. The research results show that theoretical calculations basically agree with experimental results. Compared with the aPproach based on the spectra or Discrete Wavlet Transform, our approach has advantages of fine analyzing scales, stable features and high recognizing rate. It is very suitable to identify echo signals whose spectra vary with time.

An Experimental Study on the Reinforcement of Weakly-Consolidated Shallow Formation in Deep Water Using an Epoxy Resin-Based Fluid

The mechanical properties of Portland cement differ from the weakly consolidated shallow formation in deep water.This results in undesired abrupt changes in the compressive strength and elastic modulus at the cement–formation interface.In this study,a water-borne epoxy resin was applied as a strengthening material to reinforce the weakly consolidated shallow formation and protect the cement sheath from potential failure.The mechanical properties of the unconsolidated clay were tested,including their changes with increases in the temperature and curing time.In addition,the effects of the seawater,cement slurry alkaline filtrate,and saltwater drilling fluid were evaluated.As confirmed by the results,the strengthening fluid was excellent at reinforcing the unconsolidated clay,with a compressive strength of 2.49 MPa(after curing for 7 days),even at a dosage of 5%.A cement slurry filtrate with a high pH was suitable to produce the required strengthening of the formation,especially its early age strength.It should also be pointed out that the used fluid exhibited good compatibility with the saltwater drilling fluid and seawater behaved well as a diluent for the strengthening fluid.

Eff ect of Cementation on Calcium Carbonate Precipitation of Loose Sand Resulting from Microbial Treatment

Microbe-induced calcite precipitation is a sustainable improvement technique for sandy soil, which can alter the properties of sand via microbial activity. In this study, we investigated the loose-sand-consolidation effect by controlling the injection velocity, bacterial and cementing-solution concentrations, and hold times. The results demonstrate that, as the cyclic batch increases, the utilization rate of the bacterial fluid increases and both the optical density (OD600) of the bacteria and urease activity decrease. Moreover, it was determined that a 3-h hold time for a 0.5 mol/L cementing solution with a cementing fluid velocity of 2 mL/min has the greatest bonding effect. The final strength of the loose sand with an increase in calcium carbonate content was further discussed. © 2017 Tianjin University and Springer-Verlag GmbH Germany

Physio-chemical interaction of Ethylene-Vinyl Acetate copolymer on bonding ability in the cementing material used for oil and gas well

Effective bond of cement sheath to casing or formation depends on higher tensile strength and lower young's modulus which are a measure of its ability to withstand deformation under load without parting.This work utilized Ethylene Vinyl Acetate(EVA)redispersible polymer powder as additive in the class G cement to characterize bonding ability.Tensile strength was measured for samples cured at 90°C for 3 days,whereas compressive strength was measured for samples cured at 120°C for 1 day and 3 days under atmospheric pressure.The results showed that,with the addition of beyond 10% by weight of cement(BWOC)of polymer,not only tensile strength was improved,but also reduced young's modulus.Addition of EVA additive beyond 10% BWOC showed significant benefit of flexibility in the cement system.FTIR(Fourier Transform Infrared Spectroscopy)indicated that presence of high VA(Vinyl Acetate)has no effect on polymerization of Silicates,which shows it does not hider in the formation of C–S–H phase.Intensity of chemical bond augmented with longer curing time and increased polymer content,as seen in O–H stretching vibration at 3434 cm^(−1) and from Carboxylate anion at 1571 cm^(−1) to confirm on hydrolysis.Mercury Intrusion porosimeter(MIP)showed significant reduction in fraction of mesopore sizes within the cement matrix,with the polymer addition.