Technology of Dynamic Kill Drilling for Drilling in the Superficial Layer of Deepwater
Authors: Geng Jiaojiao , Zhou Changsuo , Zhao Qin 
Published: May 2016

With the development of deepwater oil exploitation, more and more complicated problems happened and some common drilling technologies can not meet the demands of deepwater drilling. Some new technologies had been developed for deepwater drilling.

Since the well control system has not been installed, many complicated drilling problems will happen if the shallow gas (water) were encountered while drilling in the superficial layer of deepwater. Well kick is one of the drilling problems. If kick happened, drilling, running casing and cementing will be difficult. The well-bore may collapse or abandoned if the kick were not controlled well. All of those above will threaten the safety of crew and drilling equipments seriously.

Dynamic kill drilling (DKD) is one of the critical technologies for the deepwater drilling, which can solve the safe problem of the superficial layer drilling in deepwater effectively. The theory, key technology parameters and main equipments of DKD have been introduced in this paper. Based on the actual project data and DKD technology parameter design method, the parameters of kill mud density and pump rate had been optimized by numerical simulation method. The variation regulation of killing parameters had been concluded which under a certain condition of formation pressure and casing programs. The effect of hole diameter on well control procedure had been suggested too. Series analysis results can be the foundation of DKD operating diagram board and can supply an optimized design method of DKD parameters.

Introduction

There is often shallow gas or flow with relative high pressure buried in the shallow formations of deepwater. Due to the short time of sediment and the low compaction, the formations with shallow gas or flow are generally characteristic of high permeability. During the deep-water drilling, there are any risers or intermediate casings for the interval of shallow formation. Therefore, since the column pressure of drilling fluid can not balance the formation pressure, once encountering the shallow gas or flow, the fluid with high pressure will expend to the low pressure area in a high speed, and then form into the shallow kick, which occurs quickly with big expansion of gases, resulting in a series of problems, such as difficulty in drilling, running the case, cementing and so on.

Hence the well control is very critical before running the intermediate casing and installing the blowout preventer. The DKD is a new method to realize effective well control, which has widely been paid attention to since it was introduced. The DKD is to mix the seawater into the weighted drilling fluid to form a series of drilling fluid with different density based on a certain percentage, and then to pump the weighted drilling fluid into the wellbore with high speed. Its operating principle is:

According to the actual operation requirements, the pre-weighted mud will be mixed with the drilling mud (or the sea water), and then the kill mud can be mixed by an equipment which can control the mud density automatically. Then the killed mud will be pumped into the wellbore with a proper density.