Borivoje Pašić

OPTIMIZATION OF THE CEMENT SLURRY COMPOSITIONS WITH ADDITION OF ZEOLITE FOR CEMENTING CARBON DIOXIDE INJECTION WELLS

Well integrity related to carbon dioxide injection into depleted oil and gas reservoirs can be compromised by corrosion which can affect casing, downhole and surface equipment and well cement. Impact on well cement can cause overall degradation of set cement and lead to migration of carbon dioxide back to the surface. Thus, special types of cements should be used. One of the acceptable solutions is application of cement blends based on a mixture of Portland cement and pozzolans. The present paper deals with optimization of the cement slurry design containing zeolite which is nowadays widely used due to its high pozzolan activity potential. Cement blends containing 20%, 30% and 40% zeolite clinoptilolite were used. Cement slurries were optimized for application in slim hole conditions on CO2 injection wells on Žutica and Ivanic oil fields in Croatia (Europe), where an old and deteriorated production casing was re-lined with new smaller sized one. Results obtained by this study suggest that cement slurry containing zeolite can be optimized for application in well conditions related to CO2 injection and underground storage, ranging from a slim hole to standard size casing cement jobs which leads to an improvement of well integrity related to CO2 injection.

Risk Planning and Mitigation in Oil Well Fields: Preventing Disasters

Lost circulation presents one of the major risks associated with drilling. The complete prevention of lost circulation is impossible but limiting circulation loss is possible if certain precautions are taken. Industry experience has proved that is often easier and more effective to prevent the occurrence of loss than to attempt to stop or reduce them once they have started. The problem of lost circulation was magnified considerably when operators began drilling deeper and/or depleted formations. A strategy for successful management of lost circulation should include preventative best drilling practices, drilling fluid selection, and wellbore strengthening materials and remedial measures when lost circulation occurs through the use of lost circulation materials. In this paper the authors present lost circulation zones and causes, potential zones of lost circulation, excessive downhole pressures causes, preventive measures, tools and methods for locating loss zones and determining the severity of loss, lost circulation materials, and recommended treatments.

Application of Artificial Clay Samples (Pellets) in Laboratory Testing of Shale/Drilling Fluid Interaction

Wellbore instability was and is one of the most frequent problems in petroleum industry, especially in the drilling operations. It is mainly caused by the shale formations which represent 75% of all drilled formations. The wellbore instability problems involve tight hole spots, wellbore diameter enlargement, the appearance of cavings, the inability of carrying out wireline operations, poor hole cleaning, unsuccessful wellbore cementing operations and other. The wellbore instability is the result of mechanical and physico-chemical causes mostly acting concurrently. The shale instability basically comes out of its mineralogical composition (especially clay minerals content) and physico-chemical properties. Shale-mud interaction includes water/ions movement in and out of the shales due to pressure differential, osmosis, diffusive flow and capillary pressure. Many research activities about shale instability causes and shale properties (affecting shale behavior) definition have been carried out by now. Different shale samples, laboratory equipment and inhibitive muds have been used. Laboratory tested shale samples are provided by the wellbore cores, surface sampling or, which is the simplest method, by collecting the samples at the shale shakers during drilling operation. The amount of these samples is not enough for laboratory testing. Another problem is closely connected to sample quality and preservation. There are also differences in drilling fluids used in these laboratory tests, especially in their composition (sometimes containing more than one shale inhibitor). It is difficult to compare test results and conclusions made by different authors. The laboratory study presented within this paper are done with artificial clay samples (pellets) made by compacting the powderish material containing exact quantity of quartz, montmorillonite and kaolinite. The laboratory testing is done by treating the powderish samples inside the desiccator (24 hours), compacting (30 minutes), swelling (24 hours) and drying samples (24-hour). Sample swelling is tested by using different mud types and the sample mass is measured in each above mentioned phase. Special attention is directed to preparation and pellets content definition as a good replacement for the original shale in laboratory testing of shale and drilling fluid interaction. The influence of used muds on the total pellet swelling and swelling intensity, especially at the early phase of testing was determined.Copyright