Seismic Structural Interpretation

Geological understanding:

Ameyem Geosolutions firmly believe that it is catastrophic if anyone attempts seismic interpretation without having thorough understanding of Geology of the study area. Understanding of Geology of the area tremendously improve that quality of interpretation and reduce lot of possible uncertainty in the final output. Thus Ameyem would like to invest considerable amount of project time in understanding the Geology of the area by studying various data such as earlier regional geological studies which include outcrop study, depositional environment, structural evolution of the area, core analysis and any of geochemical surveys and Geophysical surveys including Gravity, magnetic and electromagnetic and seismic surveys.

Data QC & Conditioning:

The quality check and conditioning of the seismic data is far most sought aspect of any interpretation work. The Acquisition and processing reports shed light on various artifacts of the data which need to be taken care while interpretation. It needs to be checked whether further simple processing of data can improve the quality of data in question at a certain degree. Ameyem has sufficient tools to check data on various aspects. There might be the cases of over-migration, under-migration and excessive filtering on final data. Seismic data output at various stages will help to understand the data better. Thus it is requested to provide all available data for the interpretation.

Project creation:

Before loading the data, project needs to be created with the right geographical coordinate reference system (eg. UTM84-47N), project reference datum and the units.

Data loading, datum correction and mis-tie analysis& correction:

Processing report and ascii header of the segy may provide the seismic datum and the replacement velocity which has been taken in processing. These values are sufficient for the seismic data loading and datum correction. Mistie analysis and the correction required to level the seismic to legacy seismic be calculated and applied.

Synthetic tie:

The following steps will be carried out in the process of well synthetic to seismic tie:

• Analysis of regional velocity data
• Construction of T-D relation in wells
• QC of Sonic and density logs Frequency analysis of seismic data
• Construction of Syntetic seismic in the well
• Synthetic tie with seismic using various tie criteria
• Modified T-D relation output

Pre Interpretation analysis:

It has to be decided whether fault or horizon interpretation to be carried out first by looking at various aspects of data and objectives. Interpretation need to be designed in an optimum way to yield best results in minimum time frame.

Time line for interpretation:

Once the pre-interpretation analysis done, tight timelines should be synthesized to carry out the work efficiently.

Horizon interpretation:

Once the well to seismic tie achieved sufficiently, the events to be picked need to be decided. Depending on the number of horizons to be interpreted and the purpose of particular horizon- decision on event to be picked will be decided. Picking method will be decided depending on the quality of the event to be picked. QC to be carried out looking on random and arbitrary lines during the picking or soon after completion of the picking.

Suitable event identification for horizon picking:

It is not advised to stick to the place where the well top falls on the seismic while picking the representative horizon. Many times it turns out to be a costly afire. Well marker may not fall exactly on peak, trough or zero crossing. Interpreter need to exercise best practice to choose an event for picking. Seismic event quality at well may be good but at rest of the area the quality of event may deteriorate. It is better to sufficiently scan the seismic data before choosing an event to pick.

Auto picking, Guided picking and manual picking:

Auto picking may not work always and many times data doesn't even look good for manual picking. It is entirely at Interpreter’s discretion to decide which method to use at which place.

QC of interpretation with various attributes:

Time to time checking of pick on arbitrary lines is best approach rather than QCing at the end of the interpretation. Extraction of various attributes such as event quality, confidence, amplitude, dip and azimuth help not only as a quality check but also to interpret faults and fractures on seismic volume.

Fault interpretation:

Check for the discontinuous events and check whether that discontinuity suggests the presence of fault or fracture. Horizon attributes will help to easily identify the faults in case of seismic volume. Variance cube, ant-track are good techniques in case of superior quality seismic and when the detailed interpretation is the objective. It should be clarified in objectives whether advanced fault picking techniques to be used.

Post stack Attributes:

Post stack attributes provide great help in fault and facies interpretation. We have plenty of experience in utilizing post stack attributes to produce best output.

Stratigraphic Interpretation:

Facies analysis and sequense stratigraphic interpretation can add immense benefit to many exploration and development blocks. We can offer best in the industry at minimal costs.

Time structure maps and isochrones:

Time maps generation usually fairly easy job. But when dealing with sparse data, the stucture maps tend to be very far from reality. This is because seimic interpretation alone cannot capture the subsurface reality. In such situations interpreter needs to think of using other information such as surface geology, gravity & magnetic maps or anologus maps etc. We mastered the technique and can produce maps with close to reality.

Time depth relation construction:

Depending on the type of data availability interpreter needs to decide a best way to construct T-D relation in order to produce high quality depth maps. Interpreter also can use defferent method to arrive at a range of depth maps to capture the uncertainity in depth prediction. Here we see three usual ways in which interpreter produce the T-D relation.

Velocity modeling:

Velocity modeling is important aspect in the cycle of seismic interpretation. Seismic velocities conversion, well velocities utilization and corrections- everything affects the final output. So, experienced interpreter only can generate a reliable velocity model.

The best workflow which Ameyem followed to build velocity model is given below. This workflow is best suited for every developed or exploration block. Depending on the client requirements Ameyem can deviate from this workflow if need be there.

Stuctural model bulding:

Once the Velocity model ready, it would be fairly easy task to build the structural model. But it has to be seen whther the sofftware has the facility to build structural model directly from the velcoity model and time structural model. Otherwise one may need to first get the time surfaced converted to depth, then the resultant surfaces to be used to build the depth structure model.

Uncertainties in interpretation and depth conversion:

These are specific to the work we carried out

• Both new and old 2D Seismic lines are less supportive over the crest and axial planes of anticline as well as considerable distance at either sides of the back thrust. Events are not continuous thus allow interpreter imagination at those places.
• The absence of VSP/Check-shot is a drawback to address uncertainty in velcoity/T-D relation over anticline crest and across the back-thrust which causes imperfect predictions of key horizons near crest.
• Large velocity variation as observed in seismic RMS velocity across back thrust and poor horizon picking near sub-thrust zone causes large uncertainties in depth prediction of key horizons in sub-thrust zone.

Seismic Interpretation is the most valuable and deciding factor in the life of a field and it plays a crucial role in petroleum industry. Identification of useful events is as important as picking them in less time with highest possible quality. We at Ameyem invented ways to make it possible with our immense experience not only in conventional interpretation but also with different approach. We promise to deliver highest quality output to our clients.

Seismic Interpretation deals with range of issues to realize the final out come of depth maps, structural model and the volumetrics. Ameyem people with their rich experience deliver excellent output each of the tasks involve in interpretation. We provide timely outputs with excellent quality and apply state of the art technology for some of the tasks like generation of missing logs, facies analysis etc., using Machine Learning tools.

Petroleum Industry and Mining Industry face different kind of problems at different times. We at Ameyem are equipped with smart tools to tackle all sorts of problems faced by industry. Ameyem not only provide conventional solutions like, Seismic Data interpretation, Petrophysical Analysis, Rock Physics, AVO analysis but also provide solutions to those problems with unique requirements, such as Well log digitization, Seismic signal digitization from hard copies. We employ various Machine Learning techniques to address specific problems of industry, such as missing log generation, un-recorded log generation, petrophysical log creation using core samples and wireline logs and seismic inversion with ultimate quality.