Abstract
Using drilling fluids with optimum density is one of the most important approaches to stabilize the pressure of the bottom formation and prevent blowout through the drilling process. One of the common methods for this purpose is adding some additives with high specific gravity to the drilling fluid to tune its density. Among the possible chemicals, barite and hematite with the density of 4.2 and 5.2 g/cc are the most common additives. Unfortunately, although the application of these additives is advantageous, they have some drawbacks which the most important one is separation and settlement of solid phase called barite sag. The barite sag comes from barite, or other dense materials particles deposition resulted in undesired density fluctuations in drilling fluid can lead to mud loss, well control problems, poorly cementing and even pipe sticking which occurs in severe cases. With respect to these concerns, the current investigation is concentrated to obtain the relation between the dynamic conditions such as flow rate (0.308 and 0.19 l/s) and deviation angles of 30°,45°,60° and 90° and barite sag phenomenon through a flow loop equipment. Besides, the effect of drilling string rotational speed (70 rpm) on the barite deposition is investigated. The results not only indicate that increasing the flow rate from 0.19 l/s to 0.308 l/s can reduce the deposition rate, but also increasing the deviation angle from 45 to 60 o enhance the barite deposition to its maximum value.Graphic abstract
Highlights
Drilling is one of the most critical hazardous processes in the oil industry which its safety is an undeniable desire moving the researchers toward drilling fluid with controlled morphologies which can guarantee the safety and quality of this process
The experiments performed by Skalle et al (1999) show that the barite sag phenomenon can occur under both dynamic and static conditions the precipitation boosted under dynamic condition
The results reported from a systematic investigation performed by Nguyann et al (2009) with the assist of a stream loop apparatus revealed that it would be possible to substantially reduce the barite sag phenomenon if the drill string rotational speed set as a low value
Summary
Drilling is one of the most critical hazardous processes in the oil industry which its safety is an undeniable desire moving the researchers toward drilling fluid with controlled morphologies which can guarantee the safety and quality of this process. Barite sag is a well-known problem, there are limited tools which can help petroleum men to reliably detect this problem In this way, several investigations have performed to find the effect of weight mud, pressure of vertical pipe, torque, decrease and increase in mud volume and changes in rheological properties, but no consistent results make it necessary to perform more systematic investigations regarding this phenomenon for more clarification (Mirjevardi, 2017). Roohi (2011) studied a new experimental method to evaluate static sag in without using weight of the samples which is a tedious and costly approach In detail, he proposed a method which was based on the pressure measurement at the desired depth at the laboratory scale and correlates it to barite sag which directly can reduce the required time and cost due to its simplicity
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