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.
The operator was drilling their first high-pressure high-temperature (HPHT) exploration well with narrow pressure window in a swamp area of East Kalimantan. The gas field was discovered in 1977 and production started in 1990. Since then, more than 1500 wells have been drilled in this area yielding a total gas production of 9.7 Tcf. Currently T field enters established mature field status which has quite marginal reserves. Therefore, further exploration is seen as one of the solutions to locate additional reserves to enhance overall gas production. The well was drilled directionally with no offset well nearby. While drilling the 6-in open hole section, an unexpected high-pressure zone was penetrated. The zone condition was made worse by lost circulation and a high gas reading. Two cement plugs were placed using a managed pressure cementing with pump and pull method. The first plug was set by applying surface back pressure (SBP) to maintain equivalent bottom hole pressure (BHP) between lowermost pore pressure (PP) and fracture gradient (FG) at the previous shoe. After pumping 1 m3 of cement into the annulus, pump and pull operations commenced. While performing post job circulation on the first plug, it was observed that the returned fluid density at surface was less than original mud weight, indicating the possibility of contaminant invasion from formation. After waiting for the cement to reach 500 psi compressive strength, pressure buildup was observed when annulus was shut-in, indicating an inadequate pressure seal across the cement plug Applying lessons learned from setting the first plug, new design considerations were implemented such as increasing cement volume in the annulus to 4 m3 prior to the pump and pull operation to minimize cement overlapping risk and applying SBP at BHP near FG. A contingency plan was in place to determine the appropriate SBP value to be applied whenever the pumping rate was changed. A second plug job was performed safely and flawlessly by achieving the top of cement as desired. A successful inflow test was performed with indication of no contaminant invasion nor pressure bypass around the cement plug. The rig was able to continue its next operation to sidetrack the well. This paper presents the design considerations, methodology applied, and lessons learned two managed pressure cement plugs using pump and pull method in a well bore with a narrow pore-frac window where the new techniques were implemented to enhance success of the plug job despite the complexity and risk inherent with an underbalanced operation.
Seguni field and Sejadi field are smaller regions of Sepinggan field in offshore of East Kalimantan, Indonesia, which were drilled and developed by the operator since 1977. Seguni-V (redrilled well) was prognosed to encounter several depleted sandstone formations with reduced pore pressure due to produced hydrocarbons. Consequently, the utilized drilling fluid density was set as low as reasonably practical and this methodology had successfully prevented any lost circulation event until the total depth (TD) was reached. Nonetheless, the risk of losses were greater in the cementation phase of the 3 1/2-in tubing due to long column of cement (>7000 ftMD) required. Therefore, the challenge was to reduce the cement slurry density that still can achieve a required compressive strength within timely manner. The reduced slurry density was also predicted to be instable downhole due to the immense bottomhole pressure, which might crush the conventional cenospheres in the slurry as lightweight materials and result in an increase of downhole slurry density. Therefore, to minimize the risk of induced lost circulation caused by slurry density increase, a novel lightweight material with highly-crush resistant property was proposed. The result of the job with this cement system was satisfactory with no losses occurred and the targeted intervals were covered with good cement. Sejadi field, on the other hand, had experienced losses while drilling, from seepage losses which were commonly found, up to 170 bbl/hr of loss rate at one of the wells in the field. A particular lost circulation case with persistent loss rate into depleted formations was observed at Sejadi-X well. 728 bbl of synthetic based mud (SBM) had been lost into the hole when a loss rate of >40 bbl/hr was encountered while drilling 8 1/2-in open hole (OH) section. The loss rate could not be reduced even after spotting three times of 30 bbl conventional lost circulation material (LCM) pill and had cost significant volume of SBM and LCM amount lost to the formation, as well as 2 rig days spent in attempt to cure the loss. The study of the previous failure on similar problems in the neighboring well led to the solution proposal to use engineered, optimized fiber in cement slurry for lost circulation plug. The result was prominently effective and drilling operation could be resumed to total depth. This paper describes the features, case histories, challenges, field applications, as well as the acknowledged results of mentioned technologies. Lastly, this paper also introduces a mutualistic technical feature when the two technologies are combined to both prevent and mitigate lost circulation.
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