Non-Productive Time Reduction during Oil Wells Drilling Operations

Often there is no well drilling without problems. The solution lies in managing and evaluating these problems and developing strategies to manage and scale them. Non-productive time (NPT) is one of the main causes of delayed drilling operations. Many events or possibilities can lead to a halt in drilling operations or a marginal decrease in the advancement of drilling, this is called (NPT). Reducing NPT has an important impact on the total expenditure, time and cost are considered one of the most important success factors in the oil industry. In other words, steps must be taken to investigate and eliminate loss of time, that is, unproductive time in the drilling rig in order to save time and cost and reduce wasted time. The data of six oil wells were approved for the purpose of the study, where it was noted that there are many factors affecting the NPT, which differ from one well to another. Its impact was limited to drilling rig, mud pump and equipment failure. There is also a difference between the planned program and what is actually happening on the ground, due to several reasons, including human errors during the implementation of the drilling program and others due to technical errors, Misuse of equipment, in addition to human errors related to the failure to implement the drilling program.


Introduction
The NPT is definite as the time that the drilling process stops in an unintended manner or at what time the drilling penetration rate converts disproportionately low. Some researchers assumed the huge costs in oil and gas exploration projects and worked to find ways to reduce those costs, [1]. Consequently, decreasing the NPT have a duty to progress drilling performance and decrease drilling cost to save time and money. The NPT theory taking place in the 1960s, and since at that time numerous studies and lines arose in an effort to decrease lost time to satisfactory standards [2]. Drilling is tracked according to convergent agendas and delaying intended to resolve these problems [3]. This is called non-productive time (NPT). Problems that occur during drilling can be avoided from time to time by selecting the appropriate equipment and implementing the drilling program in a literal manner, in addition to a quick and accurate solution to problems if they occur. [4]. Drilling is one of the most important things, composite and expensive operations in oil well industries. Although drilling budgets indicate roughly half of well costs, less than half of the entire drilling time is consumed in real drilling operations and the rest goes as NPT such as drilling operations difficulties, rig drive, equipment failure, drilling fluid circulation [5]. From development managing viewpoint, drilling process should continuously be on agenda and on low-priced. Existence of drilling problems lead to postponement frequently push drilling action overdue the schedule [6]. The incidence of NPT and imperceptible lost time not only reason for undervalued finances but also consequence in postponements of the hydrocarbon production [7]. It was revealed that NPT can be avoided by using and following an optimal drilling program that includes all the drilling process, including equipment and personnel [8]. The method for working with statistical data that organized comparatively fast as associated to manual preparation approaches, in order to estimate the NPT for each well and reduce it as much as possible [9]. The determination of their revision is to guarantee that a balanced budget is going to be attained, by means of forecasting the drilling time predictions as precisely as conceivable. It was noted that the causes of NPT are frequent and most related to drilling equipment for instance a similar NPT incidence can occur in drilling rigs working in proximity to each other, merely since the lesson learned has not been deliberated with the rig team(s) [10]. It should also be taken into account that the drilling stage is one of the most important and costly stages in the oil industry, adopting a suitable drilling fluid is also one of the most important factors in reducing NPT and preferably not harmful to the environment [11]. The drilling performance observing projected in this revision permits the right employment of the composed drilling data in a prearranged way. This study presents an analysis of the drilling time of 6 wells that were drilled in a field in southern Iraq, in order to benefit from its data and to identify the most important reasons that led to NPT. The time taken

Methodology
Non-productive time analysis has been shown to have many advantages in many industries. On the other hand, this concept is of great benefit to engineers in many fields, especially in petroleum engineering. To achieve the desired objectives, downtime data composed fromsix different rigs are repeatedly analyzed to find the origin reasons of unproductive time. For the large number of data and its diversity, a statistical program was used to facilitate the analysis and processing. Data were analyzed qualitatively and quantitatively using Excel, the statistical program (SPSS), and the Regression Model. Descriptive statistics were used to display the results tabulated in frequency scatterings, fractions, and diagrams. Regression analysis was used to establish the relationships between the independent variables (rig, pump, drilling fluid, geological challenges, equipment failure, cement and top drive) and non-productive time during drilling.

Regression Model
Equation (1) shows the most important factors that were used to find NPT.

NPT = α + β1EF + β2 C+ β3B + β4TD + β5C + β6WC+ β7DF+ β8DM+ ε (1)
Where: α and β are constants, ε represents an error term. Each well is drilled using a specific platform and equipment from different origins, in addition to the multiplicity of companies that drill those wells, all of which leads to some differences between the NPT values from one well to another. The developed statistical program was used to calculate the total NPT hours for each drilling rig for each process and then divide it by the total operating time using the equation2.

P = NPT/ Normal Operation Time (2)
where P: frequency of occurrence (probability) of an NPT.
Equation 3 was used to apply drilling time data for different activities.

T i = (D rd / D ad ) *t i (3)
Where: D rd : Drilled reference depth, D ad : Actual drilled depth Ti= The planned number of working days for the first section, and ti = the actual number of days spent in the first section.
On the other hand, well problems are related to each other by evaluating well problems using the equation 4 of percentages of unproductive time.
Where: WP NPT-Cont.-i is the well problems nonproductive time percentages .

Conclusions
The main objective of this research is to find out the root causes of NPT and then find appropriate solutions to reduce NPT and as below: 1-Excavation problems must be taken into consideration during the planning process in order to minimize wasted time. The case study proved that there was a huge waste of time that occurred due to improper planning in addition to the use of bad and inappropriate equipment.
2-The planning program for drilling procedures can be derived based on drilling experience and equipment performance while drilling previous wells. In addition, attention to planning detailed procedures during each process and activity, and this can control the risk of wasting time during all stages of drilling.
3-Time consumed on actions for instance tripping for bit and BHA alteration and correspondingly reaming due to a pointed formation may be significantly reduced by using excellence bits' types. The consequences of this study exposed huge amount of NPT related with drilling operations for six well in south of Iraq.
4-It exhibited that the typical total NPT is 44%, while only56% of the entire drilling period is creative time. In drilling operations, it is possible to reduce the NPT, for example, when choosing the appropriate bit and the suitable equipment with high durability, and that will certainly lead us to reduce the NPT and unnecessary costs.
5-In order to have the most efficient time to operate any equipment or machinery, it is necessary to have a deep knowledge behind the causes of equipment failure and this certainly comes from the experience and competence of the company producing that equipment and tools to reduce NPT time to the nethermost level.
6-Depending on the results obtained, it was found that the NPT for wells 1 and 2 was about 17%, for well 3 it was 19%, for well 4 it was 0% and it is considered the lowest among the wells studied, for well 5 it was about 6% and for wells 6 it was 41% It is the largest of the wells that have been studied.