Lost circulation remedial techniques will be effective when they are tailored for the specific challenge. Examples of factors that govern the remedial technique are the type of losses (induced vs. natural fractures, permeable formations, etc.), characteristic size of loss zone, difference between equivalent circulation density and pore pressure gradient, etc. Typically, localized workflows are designed based on experience from wells where these factors are within certain limits. These workflows are limited to the new wells where these factors are within the same limits. Additionally, these workflows usually involve the selection of certain type/size of lost circulation materials (LCMs) with less emphasis on tuning fluid density, rheology, and pump rates. A comprehensive approach, one that caters to a wide range of loss scenarios and allows tuning all engineering parameters available for tailoring the unique solution is needed.
The work method discussed herein is built using the principles of mass and momentum conservation. These hydraulic calculations also account for rheology changes due to temperature. The domain of analysis is both the wellbore and the loss zone. Thus, any changes in the wellbore will impact the loss rate and vice-versa. To such a two-way coupled system, a cake buildup model is added in the loss zone to describe the role of filter cake resistance on loss rate. Thus, the proposed method is the most comprehensive approach available to model losses based on wellbore pressures, temperatures and plugging of the loss zone. Such a method allows for greater design flexibility to the engineer in tailoring wellbore fluids during drilling or cement operations.
The proposed method is used to understand the sensitivity of the loss zone size to the loss type, loss rate and the depth at which losses occur. This helps engineers highlight the critical information needed from job location to tailor the remedial treatment. The effect of loss zone size on the efficacy of an LCM is demonstrated by evaluating the performance of LCMs of different size and shape. This analysis is useful in tailoring blends made up of different LCMs. Moreover, this work method is used to also compare the impact of rheology and density modification vs. LCMs addition on loss control. This provides greater flexibility in tailoring different aspects of wellbore fluids and placement characteristics.
The understanding gained from the above analysis is used in predicting the loss control performance across multiple jobs. These jobs varied in loss rate and loss type. The proposed methodology presented herein revealed an optimum match with actual field observation for all the evaluated jobs. For an example job, the model was able to predict the observed surface pressure. All this analysis further demonstrates the capability of the work method in combating losses by tailoring different aspects of a cement job.
