More than 50% of our hydrocarbon reservoirs are carbonate. Despite their importance as prolific reservoirs and enormous efforts made to understand and characterise them, there are still major challenges related to drilling, evaluation, and production. Geologically and unlike clastic sediments, carbonate deposits are transported only over very short distances or form in-situ through the growth of organisms containing calcareous skeletons. Subsequent processes such as cementation, compaction, dolomitisation, and dissolution caused considerable changes in the properties of the rock, e.g. pore space and permeability and also in composition. Altogether, the primary depositional processes and the secondary changes caused a broad variety in fabric which may vary over short distances; thus have to be understood in order to evaluate reservoir characteristics. This session will summarise the current status with respect to the characterisation of carbonate reservoir rocks. It will include the geological processes responsible for the formation and alteration of carbonate rocks, the associated variations in petrophysical properties at different scales, and also the effect on chemical composition.
Geomechanical factors affect every stage of the reservoir lifecyles, from predicating drilling risks in the first well to maximising recovery from mature assets. Geomechanics enable predicting wellbore and reservoir deformation/failures and generate engineered solutions for optimal field development. Without a strategy for avoiding or minimising potential problems, reservoir development can be very costly. In general, preliminary models are used to help in setting contingency strategies before drilling and production and as new data are acquired the models are updated, refined, and calibrated to make better decisions in developing and managing the field lifecycles. This session provides a brief introduction to geomechanics in carbonate with the latest mechanical earth modelling techniques that integrate the field data with core data to help in reducing the uncertainties for better-informed decisions.
This session will focus on some major formation damage mechanisms and stimulation methods applied in tight gas carbonate reservoirs. One of the major formation damage effects that occurs during production from tight gas carbonate reservoirs is condensate banking and/or water blockage. The diagnostic techniques to identify condensate banking and water blockage as formation damage effects and the methods to mitigate them will be discussed in this session. The main stimulation techniques are used to improve production from tight carbonate reservoirs include matrix acidising, acid fracturing, and proppant fracturing. Hydrochloric acid is generally used to create wormholes or etched fracture as main mechanisms for matrix acidising and acid fracturing respectively. Proppant fracturing is an alternative option that has been applied in carbonate formations. However, there is no quantitative method to provide an answer to select the method of stimulation: matrix acidising, acid fracturing, or proppant fracturing. The petrophysical properties and the effect of elastic, plastic, and creeping deformations of carbonate formation should be investigated to identify the most appropriate stimulation technique in tight carbonate reservoirs. This session discusses how the stress-sensitive formations like tight gas carbonate reservoirs should be carefully examined especially the petrophysical, geomechanical, and fabric texture properties and their variation with the introduced fluids to determine the most effective stimulation treatment.
Well stimulation is performed using matrix acidising and hydraulic fracturing techniques. Matrix acidising is becoming an important technique to increase reservoir interface to the wellbore that improves productivity index. Research is being performed to improve wormholing efficiency to increase the stimulated reservoir volume and therefore increase well productivity. However, understanding acid penetration into the reservoir formation and imaging its penetration remains a major challenge. On the other hand acid fracturing and proppant fracturing have been applied and largely successful in tight carbonate formations. The geomechanical properties, the elastic and plastic deformations, may be investigated to decide on the most effective stimulation method. Another area of interest is monitoring fracturing fluid intake to the formation through distributed temperature sensors (DTS) using fiber optics. Other monitoring techniques such as distributed pressure sensors (DPS) and distributed acoustic sensors (DAS) deployed also on fiber optic are showing promising potential to monitor both reservoir fluids intake and depth of penetration of the hydraulic fracture. This session will discuss these techniques and provide examples of their deployment and the benefits they provide to understand reservoir production.
Hydrocarbon production from carbonate reservoirs has in recent years been focusing on hydraulic fracturing in tight carbonates and acid stimulation techniques to improve well productivity. Geomechanics and influence of regional stresses on fracturing efficiency received increasing importance. Recent development of monitoring fracturing such as microseismic, distributed temperature sensors (DTS), distributed pressure sensors (DPS) and distributed acoustic sensors using fiber optic cables have shown promising results in monitoring and improving reservoir productivity. However, there are still remaining several technical challenges associated with tight carbonate production in gas-bearing reservoirs or heavy oil-bearing carbonates such as understanding the relationship between carbonate texture and fabric in relation to fracturability of the rock, near wellbore versus far field stresses and how they impact fracturing efficiency, acid diversion in naturally fractured carbonates, fracture initiation and propagation, imaging of fracture penetration into the rock matrix, and dynamic simulation of rock fracturing ahead of operations which will all provide opportunities for future development. The objective of this session is to provide innovative views on future directions for our industry on this important topic.