The gas and oil industry is one of the most serious and responsible activities. State of emergency in this area, in fact, should be specified only in theory. Against this background, it is important for ordinary workers and managers, as well as those who are getting education for employment in the industry related to well drilling, to know the interpretation of GNVP, as well as signs, reasons, and ways to eliminate this phenomenon. Let's start with a general description.
Decoding GNVP
The letter combination GNVP means gas, oil and water occurrences. This is the simultaneous penetration of gas and oil fluid both inside the well through the columns and into the annular external section.
Knowing the interpretation of GNVP, we are faced with a rather serious problem that may arise during drilling. It requires immediate removal. Most often, gas and oil occurrences are detected at high reservoir pressure due to excessive deepening of the face, as well as due to incorrect actions by drillers or repairmen.
Causes of the phenomenon
The admission of GNVP (interpretation - gas and oil occurrences) in production is very undesirable. Here are the main causes of this problem:
- Initially incorrect work planning. This led to erroneous actions when creating the pressure of the working solution during overhaul. External pressure forced the connecting seam of the columns, which led to GNP.
- The reason may be inside the well - it is the absorption of fluid.
- During downtime, the density of the working fluid decreased due to penetration through the walls of gas or water.
- The launching and underground works were planned incorrectly - as a result, they led to a decrease in the liquid level in the column.
- The correct time interval was not observed between work cycles. One of the main reasons - there was no flushing for 1.5 days.
- A number of rules have been violated for conducting work in the mine - for the operation, development, and also elimination of emergency situations.
- The development of formations characterized by a high content of water and gases dissolved in it is underway.
- Development of fluid absorption processes in the wellbore.
Signs of GNP
The signs of the detection of gas and oil occurrences are usually divided into two categories:
- The early ones. Typical of the flow of oil into the wellbore. Inside themselves are divided into direct and indirect signs of GNVP.
- Late. They are characteristic for the moment the formation fluid exits to the surface.
Consider the categories in more detail.
Early signs: straight
So, let's start with the direct signs of GNVP:
- Volume increase (meaning fluid has already begun to flow into the well).
- The increase in speed (increase in flow rate) of the outgoing flows of flushing fluid, when the pump flow remains constant.
- Reduction when lifting the pipe string of the fluid to be added against the calculated volume.
- Inconsistency of the above volume to the volume of raised tools.
- The increase in flushing fluid, which enters the receiving tank during the descent of pipes, compared with the calculated indicators.
- The flushing fluid continues to move along the gutter system when the circulation is stopped.
Early signs: indirect
So, indirect signs of GNVP:
- Mechanical drilling speed increased. This indicates the occurrence of depression, a decrease in back pressure on the formation or entry into easily rockable rocks.
- The pressure on the pumps (riser) has dropped. It can talk about the release of a large volume of light fluid into the annular space or the formation of a siphon. This is also a sign of a violation of the tightness of the column, a malfunction in the pumps.
- The weight of the drill string has increased. It may be a sign of a decrease in the density of the flushing fluid due to the formation fluid entering the well. And also this is a manifestation of a decrease in the friction of the column against the wall of the well.
Indirect signs are paid attention only when there are direct ones, because they only talk about possible GNPP among the causes of other problems. With the manifestation of them (indirect signs), control of the well increases. This is necessary to identify already direct signs of GNVP.
Late signs
And now there are already late signs of the problem:
- At the outlet of the circulation, the density of the flushing fluid decreases.
- Its boiling, the appearance of a characteristic smell is observed.
- A gas logging station shows an increase in gas content.
- During heat exchange with the formation, an increase in the temperature of the flushing fluid is observed at the outlet.
Problem Detection Actions
Immediately after identifying the problem, the staff begins to eliminate it. These are two ways:
- Discontinuation of oil production from the well where the oil spills are detected.
- If intensive development of the reservoir is carried out, then work on neighboring wells is suspended in order to avoid widespread problems.
First of all, the watch seals the mouth, channel and wellbore, be sure to inform the management about what happened. As soon as the signs of gas and oil and gas manifestations are established, a special brigade sets in to work - workers who have received specialized training and have the appropriate qualifications.
Liquidation is carried out using special equipment: pipes are lowered under high pressure conditions. In order to suspend GNP processes, an optimal level of equalizing pressure is created in the barrel. It can be equal to the reservoir, and exceed it.
When lowering equipment in terms of GNPP, gushing may occur. Then the team proceeds to jam it, relying on emergency routines. Additionally, representatives of the technical supervision organization are involved.
With GNVP, the well is blocked by a barite plug. It creates an impermeable screen in the layers and allows you to install a cement bridge on top. If the gas and oil manifestation is opened during the operation of two pumps, then their work is provided either from one tank or from two, but with locking devices between them.
Methods for the Elimination of GNP
As soon as the true cause of GNPI is established, it is necessary to choose one most effective way to eliminate it. There are four of them.
Well killing in two stages. The most important thing here: a clear separation of the stages of work on washing out the oil fluid with the same solution that was at the time of the discovery of the cause of the GNP, and at the same time preparing a new solution with the required density for killing. The first stage is the plug of the well. The second is the replacement of the working fluid.
Stepped jamming. It is effective when the pressure in the column in front of the throttle increases relative to the value of the maximum permissible for it (the column) or hydraulic fracture of the shoe level. First, the throttle opens slightly to reduce the pressure in the column.
Because of this, a new flow of water and gas will be observed at depth. Since the peak of the pressure formed is short-lived, the next time the throttle is opened, while flushing the well. The actions are repeated until the signs of GNPI completely disappear, normalization of peak pressure indicators.
Waiting for weight. As soon as the gas and oil manifestation is detected, the staff stops oil production, blocks the well. After this, a solution of the required density is prepared. Be sure to maintain pressure in the wellbore, which is similar to the reservoir pressure, to suspend GNP and further flooding of the oil fluid to the surface.
2-stage extended jamming. After the detection of GNVP, the fluid is washed out with the same solution. Then its (solution) density changes to necessary. The method is mainly used in the absence of suitable containers for the preparation of the required volume of working fluid. The method got its name due to the fact that the process of leaching fluids with it is somewhat more extended in time than with conventional two-stage jamming.
Education and training
According to the Safety Rules in the oil and gas industry (paragraph 97), we can establish that once every two years there is a knowledge check in the section "Well monitoring. Work management with (interpretation is known to the decryption) GNVP". The certificate is given for three years.
The foregoing applies to employees who carry out both direct work and manage processes by:
- drilling and well development ;
- their repair and restoration;
- conducting shooting-blasting and geophysical operations at these objects.
The sooner GNPIs are discovered, the greater are the chances of preventing a complication of the problem — significant downtime in oil production, which leads to large losses on the financial plan already. In order to prevent the development of gas and oil manifestations, it is necessary to pay due attention to external sensors of the volume, density and pressure of the working fluid.