Total E&P Indonesie (TEPI) has been drilling in the Tunu, Tambora, and Handil (TTH) fields located in Delta Mahakam, East-Kalimantan of Indonesia. These fields have been producing gas for some decades in Indonesia. Casing cementation over weak formations and low fracture gradients are some of the major challenges encountered during operations in these fields; hence, designing and pumping lightweight slurry systems with superior performance when compared with conventional cement slurries is required to overcome the aforementioned operational challenges. Historically, slurries in TTH have been designed with conventional cenospheres as the extender; cenospheres are a byproduct of coal combustion at thermal power plants, and, in some cases, cementing operations would either face lost circulation or sustained casing pressure (SCP) or a combination of both due to cenospheres crush and an increase in downhole density. An alternative method was needed to replace the existing cenosphere-based system and prevent lost circulation, which mainly occurs due to slurry instability and higher downhole density. A comparison study required collection of four different samples of engineered glass bubble extenders. This paper describes the results of an extensive, thorough study on different slurry designs to replace the current method with a new system to minimize the risk of lost circulation and eventually reduce the risk of SCP which, in some cases, is a consequence of lost circulation. Field implementation results of the new system confirmed an effective reduction in the number of wells encountering lost circulation during cementation. The comparison of cementation with both systems in the same field in more than 150 wells is presented in this paper to provide a case history that reflects operational improvements achieved by using the engineered highly crush-resistant cement slurry system.

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The main objective of perforating is to connect the wellbore to the reservoir zone by creating tunnels through casing and damaged zone into the undamaged rock. The process of detonating perforation charges generally causes damage due to crushed rock material around the perforation tunnels.There are different methods used to mitigate damage due to perforation, such as static and dynamic underbalanced perforation. In static underbalanced perforation, conventional high shot density perforating guns are run in underbalanced conditions in order to have clean-up after perforation. In dynamic underbalanced perforation, a specific gun design associated with gun puncher charges provides dynamic underbalanced conditions across the perforated interval immediately following charge detonation in order to efficiently clean up each single perforation tunnel from crashed rocks and debris.Using deep penetrating charges followed by a dynamic underbalanced can improve well productivity since it mitigates the damage related to perforation. Dynamic underbalanced perforation removes the crushed rocks and debris from the tunnels using a sudden pressure drawdown across the perforated interval immediately after detonating the charges.This study is intended to numerically simulate the dynamic underbalanced conditions after perforation in order to have a better understanding about the phenomenon during perforation process as well as perforation cleanup. The effect of wellbore fluid type on dynamic underbalanced behavior has been simulated to investigate efficiency of dynamic underbalanced in different wellbore conditions, and also three field examples are also shown to verify the simulation results. Introduction:The main parameters that control perforation performance are shot density, penetration depth, perforation charges phasing, and perforation tunnel diameter [1], which have been shown in figure 1. Perforation performance depends on sufficient downhole penetration, optimum phasing, shot density, and perforation skin. Deep penetration, at least 50% beyond damage, is needed to effectively connect wellbore to undamaged rock [1].As perforation charges detonate, the charge liner collapses to form a high velocity jet of fluidized metal particles. Perforating jets achieve penetration by extremely high impact pressures, typically around 3,000,000 psia on casing, and 300,000 psia on the formation [2]. Detonation duration occurs in microseconds. Unfortunately, explosive perforating pulverizes formation rock grains and causes a low-permeability crushed zone (Kc) in the formation around perforation cavities as described in

Cementation of the monobore completion strings for Total in Tunu field of Indonesia is a balancing act. The bottommost reservoir sands are within 30-ft of a high-pressure zone. Therefore, having a conventional length of shoe track, two to three tubing joints, will block the access to the bottom sands. Furthermore, any error in displacement volumes of these cement jobs would lead to costly remediation. Drilling out cement inside the small tubing sizes would force Total to use special drilling techniques, and displacing extra mud volumes would wet the shoe, which could jeopardize the well integrity. To tackle the challenges, shoe track length was minimized with the float shoe and collar placed only 1 m apart. A custom-made calibration plug, with proper burst disc pressure rating, was designed and used prior to cementation; this plug allowed the tubing volume to be measured physically. Based on observing the pressure spikes on the rig floor, the displacement volumes for all the cement jobs are known prior to the cement job. As it is proven to be valuable, this innovative cementation method continues to be used by Total ever since its introduction. The calibration plug has been used in more than 200 wells with the total depths of 13,000-ft to 17,000-ft. The cement displacement was done accurately, and top plug was bumped successfully. This has saved 100-ft—the conventional shoe track length—of drilling on each well. Also, the plug contributes to the safe exploitation of the bottom targets without encountering the high-pressure zones. This innovative technique is applicable to cementation of all completion strings with reservoir targets close to the tubing shoe. It has been proven to be a reliable method in eliminating the shoe track and can be applied to any similar cementation operations.

Analysis has consistently shown that carbon capture and storage (CCS) has an important role in meeting emission-reduction targets (IPCC, 2018). CCS wells require special design considerations to ensure long-term zonal isolation when exposed to carbon dioxide (CO2) because a complex set of chemical reactions leads to carbonation and dissolution of conventional cement sheaths. Several studies conducted into the long-term stability of different cement systems when exposed to wet supercritical CO2 and CO2-saturated water showed that the novel CO2- resistant cement system provides enduring zonal isolation. Properties investigated included permeability, porosity, mass evolution, CO2 degradation front, and compressive strength. Given its superior mechanical properties, the novel CO2-resistant cement system was selected for use in the first Australian offshore CCS Gular-1 appraisal well. To ensure that the blend characteristics of the novel CO2-resistant cement system remained optimal, a stringent quality-control procedure was developed. The blend management process, supported by rigorous laboratory testing, covered the complete lifecycle of the blend. This lifecycle extended from sourcing chemical components, to blending the components in a bulk plant, to transporting the blend across land and sea, and ultimately, preparing the slurry mixing. By adhering to the project management process, all primary cement jobs were successfully performed without incident using conventional cementing equipment and practices. The novel approach of blending the product locally at a fit-for-purpose facility reduced costs compared with previous methods of importing a preblended product prepared at a special centralized facility. Blend homogeneity was maintained during transfer from a sea vessel to the jackup rig, with minimal change in density between samples received from the bulk plant and samples received from the rig. This blending, which verified the initial blend flow capability and the robustness tests performed at a regional laboratory using specialized equipment, concluded the blend is suitable for offshore operations. Selection of a suitable cement system to ensure long-term zonal isolation will prove essential to the continuing expansion of the CO2 injection market. Through this offshore CCS appraisal project, valuable best practices and lessons learned in design and execution have been captured. This paper presents the decision process used for selecting a suitable CO2-resistant cement system for Australia's first offshore CCS appraisal well, drilled by AGR as part of the CarbonNet Project in late 2019, as well as the project management processes implemented to ensure successful job execution. The experiences detailed in this paper will benefit other operators confronted by challenges associated with wells subjected to CO2 injection.