No abstract

In an effort of maximizing the production from low permeability reservoirs in mature fields, operators often strive to implement innovative technologies and engineering approaches that can help achieve that goal. This paper presents an analysis of the temperature responses from bottom hole gauges of several horizontal wells that have been stimulated offshore Black Sea. The analysis covers the fluid cool down and heat back profile during stimulation and production. Ultimately, the analysis' goal being to better understand the rheological properties of the stimulation fluid and enhance well clean-up by avoiding miss-allocation of temperature ranges during fluid testing for when the well is brought on production. Based on available data from bottom hole gauges implemented in the horizontal wells stimulated in the Black Sea, an analysis of the temperature gauge responses has been performed. The analysis includes a workflow of temperature change validation per well, considering fluid pumped per port in stimulation phase and fluids produced per port in production phases. The fluid production allocation per port was done utilizing chemical tracer technology results. Stimulation treatments in the same reservoir offshore Black Sea, Romania have been analyzed in terms of bottom hole gauge readings of temperature during the stimulation fluid pumping and during the early production period of each well. A workflow was implemented on each well to correlate fluid per stimulation stage pumped to temperature changes during the treatments. Similar approach was used to correlate the temperature heat back profile during the shut in of wells in the initial 48 hours for proppant curing to the production phase clean-up of the wells. The observed cool down during pumping was of no surprise, but the heat back indicated a slower process of warm back that affects the stimulation fluid testing approach and the understanding of possible near wellbore pressure differentials caused by misallocation of temperature range testing of pre job rheology tests. A combination of temperature data with diagnostic tools and the pertaining analysis will provide a better description of wells' performance. In conclusion, misinterpretation of modelled cool down and reservoir heat back can lead to erroneous understanding of fluid clean up, ultimately affecting reservoir fluid inflow. Understanding the areal temperature response helped optimize fluid testing approach and plan for better clean up. The approach and the sensitivity analysis results are beneficial in understanding the temperature behavior during treatment pumping and production of stimulated wells. This process can enhance an engineer's approach in scrutinizing stimulation fluid testing for improved post stimulation clean up.

The advancement of wind energy technology brings about an increase in the size and height of the wind turbine towers. As the upscaling of the conventional steel tubular tower is problematic, alternatives are being investigated. In this paper, several configurations were reviewed and the lattice tower was identified as a possible solution. This study analyses and compares the structural performance of the two tower configurations, tubular steel and lattice, of equivalent height, stiffness and mounted rotor, in two sets of tower heights, 120 m and 150 m. The towers are mounted by the baseline 5 MW turbine developed by National Renewable Energy Laboratory (NREL). The results indicate that lattice towers are a suitable alternative to the tubular towers, providing significant material savings for a similar structural behaviour. Comparable bending moments were recorded in the base of the structures. The most demanding operating condition of the wind turbines was identified to be system braking cause by a sudden increase in wind velocity outside of the operating range. The 150 m lattice tower responds with excessive displacement during this abnormal operating condition; this is a potential issue that can cause generator failure if not accounted for in the rotor design.

This paper presents a case study of fracture interaction mitigation in a multistage horizontal stimulation of an offshore Black Sea well. A multi-faceted approach in applying lessons learned and pre-job geo-mechanical analysis of depletion-induced stress differential and its effects on fracture interactions will be discussed. Details of on-the-job, real-time bottom-hole pressure monitoring of nearby wells, with the effort of on-the-fly pumping schedule changes, will also be provided. An analysis was conducted on past fracture interactions observed from multistage stimulation jobs in the area. Depletion, distances between producing wells, and a stress analysis was performed using fracture simulation software, and a consequent analysis of fracture geometry was applied. A bottom-hole gauge pressure profile assessment of nearby wells, including the pre-stimulation, shut-in, and post-stimulation period of the targeted well, was completed. A redesigned treatment was applied, considering a mitigation plan for potential on-the-fly changes during pumping. A holistic tracer analysis of production contribution between stages and wells was performed, with the goal of understanding possible crossflow of production fluids. Past-fracture interaction events have been analyzed, and clear drivers for fracture hit communication were observed. Extreme depletion effects were a primary factor in enabling fracture communication. The preferential fracture growth was further enabled owing to the continuous production of nearby wells and no shut-in implementation. The 3D geo-mechanical model was built using pertinent data from the targeted and nearby wells. The model was further optimized using fracture geometry outputs, and constraints were input to limit the fracture growth and avoid communication. The outcome of the analysis showed a clear driving force behind the interactions was depletion. An on-the-job assessment of diagnostic tests yielded a heterogeneous behavior of the horizontal segment, further proving stress differentials along the lateral. An overall chemical tracer analysis of the targeted and nearby wells was completed using pre- and post-stimulation fluid samples. The results were crucial in understanding the stimulation approach and possible crossflow effects due to fracture communication. Additionally, using bottom-hole temperature readings, a rudimentary cool-down and heat-back analysis was performed to better understand possible fluid interactions with nearby wells and optimize fluid design. Intra-stage fracture interference presents unique events and challenges that are typically managed on a case-by-case basis, and this work presents the critical analyses that are paramount to planning stimulation treatments in highly depleted segments and reservoirs with wells in close proximity.