Development of New Kill Fluids with Minimum Sagging Problems for High Pressure Jilh Formation in Saudi Arabia
INTRODUCTION Barite sag is an unwanted variation in drilling fluid density after an extended period of static conditions. This problem is experienced frequently in Khuff and pre-Khuff gas wells in the Base Jilh Dolomite (BJD) formation. The Jilh formation is a dolomitic Middle Triassic tight zone that ranges from 8,000 ft to 10,000 ft true vertical depth (TVD) with abnormal saltwater pressure. Several factors add further complication to the problem of well control, such as uncertainty in predicting pore pressure, high temperature (300 °F), well deviation (leading to the Boycott settling phenomenon), drillpipe eccentricity and salt contamination of the drilling fluid. This high-pressure BJD formation requires a drilling fluid with a density up to 150 pcf. For high density fluids, achieving the right fluid formula with the right fluid rheology is difficult since excessive heat, dehydration and solids loading can deteriorate mud properties. The addition of weighting materials, such as barite (BaSO4) or hematite (Fe2O3), is needed to achieve the desired density to overbalance the well and avoid any possible flow from the formation; however, maintaining a high volume of solids content — of BaSO4 particles or any other material — in suspension is challenging, especially for extended periods of time. The separation of weighting material particles — usually BaSO4 — from the mud leads to undesirable density fluctuation as the drilling fluid is being circulated throughout the hole. This phenomenon, often referred as barite sag, may lead to serious well control incidents, stuck pipe, lost circulation and nonproductive time. Previous experience has shown that the barite sag phenomenon is attributed not only to mud-related problems but also to operation related practices1. Drillpipe eccentricity, stationary drillpipes, hole inclination and low annular velocities can dramatically increase barite sag2. Barite sag increases even faster as the hole angle increases to between 45° to 60°. This process was reported by Boycott in 1920, when he noticed that blood cells settled faster in inclined test tubes than in vertical tubes3.
Nanomaterial-Based Drilling Fluids for Exploitation of Unconventional Reservoirs: A Review
The world’s energy demand is steadily increasing where it has now become difficult for conventional hydrocarbon reservoir to meet levels of demand. Therefore, oil and gas companies are seeking novel ways to exploit and unlock the potential of unconventional resources. These resources include tight gas reservoirs, tight sandstone oil, oil and gas shales reservoirs, and high pressure high temperature (HPHT) wells. Drilling of HPHT wells and shale reservoirs has become more widespread in the global petroleum and natural gas industry. There is a current need to extend robust techniques beyond costly drilling and completion jobs, with the potential for exponential expansion. Drilling fluids and their additives are being customized in order to cater for HPHT well drilling issues. Certain conventional additives, e.g., filtrate loss additives, viscosifier additives, shale inhibitor, and shale stabilizer additives are not suitable in the HPHT environment, where they are consequently inappropriate for shale drilling. A better understanding of the selection of drilling fluids and additives for hydrocarbon water-sensitive reservoirs within HPHT environments can be achieved by identifying the challenges in conventional drilling fluids technology and their replacement with eco-friendly, cheaper, and multi-functional valuable products. In this regard, several laboratory-scale literatures have reported that nanomaterial has improved the properties of drilling fluids in the HPHT environment. This review critically evaluates nanomaterial utilization for improvement of rheological properties, filtrate loss, viscosity, and clay- and shale-inhibition at increasing temperature and pressures during the exploitation of hydrocarbons. The performance and potential of nanomaterials, which influence the nature of drilling fluid and its multi-benefits, is rarely reviewed in technical literature of water-based drilling fluid systems. Moreover, this review presented case studies of two HPHT fields and one HPHT basin, and compared their drilling fluid program for optimum selection of drilling fluid in HPHT environment.
Centrifuge modelling of effects of shield tunnels on existing tunnels in soft clay
With the rapid development of the subway network,the phenomena of shield tunnels going across the adjacent tunnels are becoming more and more common.The interaction between shield tunneling and nearby tunnels is more complicated than the ordinary shield tunneling in intact soil strata.Based on the project of Shanghai Bund Passage crossing Metro Line 2,the method of centrifuge modeling together with the field measurement is employed to study the effects shield tunneling on nearby strata and existing tunnels.In centrifugal model tests,the effects simulation techniques considering the unloading of excavation,ground loss and grouting are developed to analyze the longitudinal settlement of the shield tunnel and the existing tunnel induced by the shield tunneling.Besides,the deformation distribution and settlement curves of the existing tunnels during shield construction are studied by using the monitoring data.