Design and Application of Removable Plugging Slurry for Fractured Carbonate Reservoir
To meet the requirements of leakage stopping and reservoir protection at the same time in fractured formation, the removable plugging slurries with high temperature tolerance were designed, evaluated and applied in the field successfully. Analysis shows that the fibre materials can deposit onto crack surface, bridge and seal fractures quickly and the selected particles can bridge in throat near wellbore. The comprehensive grading of filling particles was determined from the point of view of gradient filling. The designed plugging slurries KJD155 and KJD200 with higher total dissolution rates sealed 1 mm, 2 mm, 3 mm, and 4 mm crack blocks effectively at room temperature and high temperature (KJD155 at 155 °C; KJD200 at 200 °C) respectively. Their pressure bearing ability of them was up to 5 MPa under bottom hole conditions, which was beneficial to the next operation. Field application of the designed plugging slurries was carried out successfully and showed that they were removable and did smaller damage to reservoir.
A Chemical Lost Circulation Agent for Severe Leakage in Drilling
This study presents a chemical lost circulation agent with some distinct advantages that make it suitable for use in controlling severe leakage during drilling process. It is a granular solid with irregular shape and able to bridge or fill the cracks and other porous or faulty formations into where the drilling fluid is lost. Then this agent will undergo a chemical reaction with water, and the reaction products fill between particles and bind tightly lost circulation agent particles to each others or to the rocks at the lost circulation zone, thus effectively enhance the compressive strength of the cementing body formed by the agent and prevent lost circulation. Temperature, particle size, and additives added have been shown to have a significant influence on the consolidating rate and compressive strength of the cementing body. In addition, the cementing body has certain permeability, and the permeability can be adjusted, so this agent is proper for use to control lost circulation in reservoir.
Physiochemical Properties of Sago Starch Modified by Acid Treatment in Alcohol
Sago starch is usually chemically modified to overcome and improve the unstable properties of native sago starch during processing. In this study, sago starch was treated in hydrochloric acid in the presence of methanol, ethanol and 2-propanol at 450C for 1 hour. Granule size, granular structure and solubility of the modified starch were investigated. Results showed that recovery yields of the modified starch were in excess of 57% with a maximum recovery of 94%, and the average granule size of the starch ranged from 24.8 to 30.1 µm. Images under light microscope revealed some internal fissures in starch granules after acid-alcohol treatment. Acid concentration had a pronounced effect on the degree of polymerization. The degree of polymerization progressively decreased as the carbon number of the alcohol increased. This study showed that sago starch can be modified through hydrolysis and alcoholysis to give various limit dextrins with high solubility.